Un-Installing XP-Pro

How do you un-install XP-Pro from a Dell Inspiron 6000? It does not show in the Remove Programs. I have had to re-install, I didnt see
where it un-installed. I belive I have XP-Pro, installed on top of a previous install, I have a 30 gig hdd, with Office 2007 Small business, Canon printer/scanner, Firefox, IE7, Adobe, reader, player, and I have just 4.71 gig left,
I uninstalled office 2007 to get rid of office 97,I noticed that I had 20 gigs being used, this seems like to much for those programs.

How do I get back to a un-clutered HDD ? I think i should have about 15 gig’s open.

Please send me step by step instructions.

Best Regards, Steven Christiansen