Hi! You have already been helped by one of the best on this site, but I may also be able to help somewhat. Is it now working for you? If not, it does sound like you've already done most of what needs to be done and the only problem you may still be having is in locating the correct downloads folder.
The part that confuses me is when you talk about how you have The Sims 2 Deluxe on one drive and The Sims 2 Pets on a different drive, but since you know your game is working correctly with this installation, then the only part we need to figure out is where the correct downloads folder actually is.
When I want to put something in my downloads folder, I first open the folder on my desktop called My Documents. Inside of that are many folders and one of them is called EA Games. I open that and inside of that I see a folder simply called The Sims 2. Inside of this folder are a bunch of folders, including a Downloads folder. This is the folder where the files you extracted from the Inteen zip need to be so the game can use them.
So, do you have a My Documents folder? If you do, are you able to find the EA Games/The Sims 2/Downloads within that folder? If not, then you will need to find this folder. When installing The Sims 2 Deluxe on the C: drive, it puts files in two locations.
The majority of files are located here: C:\Program Files\EA Games and the "play" files (the one with the Downloads folder which we are looking for) is located here: C:\Documents and Settings\UserName\My Documents\EA Games\The Sims 2 and then within this are several folders, one of which is the Downloads folder.
Due to your customized installation, I am not sure how to help you find the correct location, but I'm hoping that by telling you were mine is located that you'll be able to find the correct location.
You already mentioned that Custom Content is "open" and I'm assuming you mean that you've turned the in-game options to allow/show custom content on already and have exited once for those changes to take effect.
After reading over everything you've written, it actually does sound like the only problem may be in locating the correct folder to place the files in.
Flirting -- I think you may have an option for a very subtle type of flirting which does set gender preferences. If your sim is in a room with another sim, can you click on that sim and find an option to Check Out? I rarely use that option, but I think it is under "Flirt". You may have to first try it with another teen, but if you can find and use that option, it will set the gender preference. I'll have to go back into my game to see for sure, but I think that option did come with Nightlife.
Clean Installer is a great tool, and I recommend it to everyone. I don't know exactly what the Mod Conflict Strategy Guide says about it, but it is not actually the same as using a Hack conflict detection tool. What the clean installer will do is it will list everything in your downloads folder and any hacks show up in red. From there, you can determine for yourself whether any of those hacks may conflict with Inteen. There is also a hack conflict detection tool which you can download and use to see if any hacks may conflict. You can find one here: http://www.simwardrobe.com/ It's located under Programs and then it's the second program on the list.
If you do download and install Clean Installer, read the FAQ and possibly the Quick Start Guide to learn how to use it. Just get the top one on the list -- version 1.5.1.4.
Now I feel as though I'm rambling, lol! And I'm not sure I actually helped with anything. I'm going to go ahead and post this though and then if you have more questions, just edit your question again. :-)
Edit to add:
Sorry I didn't get back to you right away. I actually went into my game to see exactly what the option in the Flirt section was called. If your sim is in a room with a non-related sim, click on that sim and under Flirt you should see the option Check Sim Out. When you have your sim do this, it will set their gender preference, so make sure you are doing it on the gender that you want your sim to be attracted to.
Yes, you have done everything correctly and found the correct folder to put the files in -- that's why you saw the message when you opened your game.
That message is there because it is EA's way of saying, "If you put something into your game that changes the way we made it and it messes it up, it's not our fault." :-) Global hacks are not necessarily bad, it's just that they make global changes. In this case, you want those changes. I have several different global hacks in my game and it runs great.
When you see that screen, make sure you click to Enable the Custom Content. Now, if you don't want it to stop on that screen every time you start up your game, go in to a neighborhood and then go back in to the options area where you click to have the cc show in the catalog. Of course with this hack, there isn't anything that will show up, but that's the area I want you to go into. Next to the part about showing the cc in the catalog, you should see something about Showing A Dialog Box on Start-up. By default, this is set to Enabled. I always disable mine. That prevents that box from popping up each time you start the game. Then, below that you will see a white star. Click on the star and make sure the box to Enable Custom Content on Start up is checked.
Then exit your game so it will save these changes. Now go back in and play. Now is the time when you should look for the things it tells you to look for to see if Inteen is working. Since you say it mentioned the hacks, I'm sure it will be.
As Wollybutt told you, this hack is a very well made and well tested hack which should not cause you any problems. Oh, but for the future, you can also make subfolders inside of your downloads folder and put items in them. So, you could make a subfolder called Inteen and move the files into that if you wanted. Then, if you ever wanted to take them back out, all you would have to do is drag that subfolder out of the Downloads folder. I make subfolders for pretty much all the custom content I put into my game -- whether it's a hack or simply a new clothing outfit. Good luck and have fun!
Oh and I did want to tell you that not all of us are super smart with computers. When I first started playing this game, I didn't even know how to make a back up of the game files, how to use winrar or any type of unzipping program, how to locate the correct folders, etc. You learn as you play. So don't feel stupid, we all had to start somewhere, right?
Edited again to say -- I feel the same way, WB. :-) Feels good to know it's working for him/her doesn't it?
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ETA -- glad it works and that you're happy, it really does make you feel good knowing you helped someone. I wanted to help you out picking the best answer. Wollybutt was the first one to help you and she helped you a lot. Then she made sure she starred the question so someone else would see it. I think you should give her the best answer as I feel she deserves it most. :-) Have a great day and happy simming!