Well, quite frankly windows XP (actually anything from about win95 up, but especially XP) hates dos sound configs.
You can get them to work, but without looking at your device settings, control panel, and config files, I have no way to tell you which settings WILL work. All I could do is give you a ton of maybes.
Now, you didn't specify which game you're talking about here, and I honestly don't remember if FO 2 has a DOS version or not (never used any of the DOS versions personally)
So my advice would be to look at these threads first:
http://www.nma-fallout.com/forum/viewtopic.php?t=1593&highlight=installing+winxp
For installing FO 1 under XP/2000 etc
http://www.nma-fallout.com/forum/viewtopic.php?t=8423&highlight=installing+winxp
Manual install proceedure for FO 2 for XP/2000/etc
Now, another trick you might try is to set your windows desktop resolution manually before installing. If you go into the advanced section, you should be able to select a 640 x 480 mode if they don't show up on your normal sliders.
Yet another suggestion would be to look into running the DOS version (if you can't get any of this windows version stuff to work) but using DOSBOX - it's a pretty good emulator that helps out a ton with older games including getting sound support and such to work well (plus you can also use it to slow things down if need be)
You can find that here:
http://dosbox.sourceforge.net/news.php?show_news=1
Hope something in there is some help.
-Wraith
