why are you using the x86 version? :/
no one uses 32bit operating systems anymore, so you should get the x64 version of desmume.
Get the latest version from the official site here: http://desmume.org/
(get the x64 version for 64bit os)
For a drastic speed boost, open the emu and go to config > emulation settings.
Enable the JIT dynamic recompilier, and leave block size at 100. (if a game fails to load or has any problems in proper emulation of game elements, try lowering it to a lower vale such as 1-15. tho the lower the number, the less speed boost you will get from it. if it still wont work after that, you may have to disable it. not every game works with it, tho most do)
If you still need more speed, you can go to config > 3d settings. use openGL3.2 (or openGL if you use an older graphics card or chipset). It should be faster in most cases, but try both that and soft rasterizer, and use which ever gives better speed for you.
Then go to frame skip and set it to a value or 1-3 (you can go up to 4-6, but id recommend only 1-3).
Leave sound settings default, and do NOT turn on magnification filters. They improve texture quality in games, but at a VERY high cpu cost. and if you cant get full speed w/o doing above things, you shouldnt use this lol.
lastly you can set the emulator to a high priority thread (open task manager, ctrl+shift+esc, go to processes, find the emu and right click set priority. if on win8, click go to details, and on that list right click the emu and set priority). you have to do it each time you open the emu (there are ways to do it automatically by using a .bat script)
Ofcoruse you can do things like close things that are opened in background, lower windows visual effects/etc.
Doin above should EASILY get you full speed in every game. (i mean my ancient 1.5ghz core 2 dou laptop with integrated intel graphics gets full speed on everything...)