based on replies i'm thinking that the more stuff and effects etc that a theme has running, the more memory it uses. im not really too sure on what kinds of stuff there is for the different themes, but i doubt that i'll be pumping it up to 100mb lol. i think the most memory consuming thing i'd use is transparency. and possibly something to monitor system performance.

i think i have enough information now (except i dont know if it creates problems with programs that depend on windows themes like pidgin)

thank you for all of your help. i'll give litestep a shot (or 12, as my computer tinkering experiences go)