do know what you might have done wrong, but I have Windows 7 on my mini and its anything but slow, I also have XP on it too, I prefer Win 7 over XP and there is very little IF any difference in speed...too bad you feel that way, if you read other posts on this forum most people prefer Win 7....dont what could have gone wrong with yours..

PS: I also wiped that restore partition and all of the Dell diags clean too, and I have a 500gb drive so it wasnt for space...I just didnt want them....after all thats why they give you the DVDs, just copy them to a USB Flashdrive and reinstall if necessary