Hello Vanillaxtract, wow! that thread is rather old I didn't expect it to really hold out that long, but Great! to see someone trying W-7 on another marginal machine.
Well what build did you install? X-86 no doubt. You really gave only enough answeres to leave me with about 20 or 30 more questions. If you are really interested in the challenge then you should start at the bottom of the ladder. Make sure all the drivers are the best suited for the system you are running. Notice I didn't say Most Up To Date. See with an older MoBo and chipset, as well as other running gear you'll nee to be careful with drivers because some of the newest could very well be tweaked towards higher tech and newer pieces. try finding bios updates that exactly match your chipset first. then go to nvidea's websight and check out their drivers package for your video card, they have really been pretty good about getting out workable drivers for almost all their product lines. Can't say as much for Creative labs, they have been kinda slow with their audigy cards drivers but they recently put out a newer release that seems to work well.
Your next place to look at I'd recommend be
FileHippo.com - Download Free Software they are a good place to get codecs packs CCCP and K-light mega pak are both very good to work with. the hippo also has a good selection of players you can get as well. media player classic, zoom,vlc, and gom are all good choices to try and are all free. And another You can acquire that works well with the geforce card is, pure video by nvidea, though this one does cost, (eh hemm).
Right now My Mom is using that very same old dell slim-line as her main machine working with build 7100 and only 500meg of mem and its built in intel graphics chipset and though somewhat slow to load pages at times, all in all it does well with video as well as utube.
The Best advice I can give is probably; Keep up the good attitude and keep on fiddling with your settings. Do regular system restore points to be able to back up from occasional problems. And have fun fiddling.