If you want to keep your current desktop settings and all of your program settings then keep the C:\Documents and Settings\[USERNAME]\Application Data\ folder. You usually can't be logged on as that user to copy the files so you might need to make another user to do it.

Also, if for some reason you have a website on your computer, remember to make a copy of the C:\Inetpub\wwwroot folder. I made a full webapp one time and forgot that folder when I reformatted... it hurt me. :wtc:

That's the major stuff other than what's already be mentioned. Have fun.