Can i permanently clean my hard drive and still leave everything i have in favorites, bookmarks, starter page?

i'm computer illiterate but get around ok. i want to clean my hard drive completely but don't want to lose everything i already have in my e-mail, favorites, bookmarks, addresses, etc..i share my computer and also wanted to know if i clean my side will it also clean the other person's side? will i lose everything? will we both lose everything? will i lose all downloads including the one's i've purchased? can i do this without a flash card or zip drive or whatever they are called. also, are free download hard drive cleaners reliable? i'm running windows vista in a dell dimension c521. the bottom line is i want to clean my hard drive and not lose anything. i'd sure appreciate any help. thanks