My iMac is ridiculously slow

hello everyone! i've been having problem imac couple of months now. i'm writing iphone because if on imac take forever...
installed windows 7 on imac year , half ago using bootcamp play mmorpgs, did download wow on imac around time started being slow. don't think wow reason why it's being slow, stopped playing wow on imac few weeks ago slowness getting worse. pc side of computer fine though, feel mac side has virus; possible?...

specifics:
- takes @ least 5 minutes mac start up
- torrented lot of movies/shows until slowness started
- streamed movies/shows
- pinwheel of death lot
- when try click user, freezes while before can enter password
- takes long time search index

computer info:
- version 10.5.8
- ram 2gb (yeah know horrible)
- processor 2.8 ghz intel core 2 duo

me thank much, want fix problem before leave college because mom use computer, , don't want have hard time.
if need more information on computer ask, again!

 

can help?
performance tips mac os x

 

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