if you've got lots of ram, then it won't make your windows work slower. i've got 128 megs of ram and it's fine for me.
i think that patchXP is better than styleXP. if you've got trial version of stylexp, then after 30 days it's going to ask registration and you cant use it anymore. but the good side stylexp is that you can switch logons with it.
patchXP is simple. you patch it, click reboot and then start downloading themes.