Unusually Slow Computer

[colonel1]

Hello. I am running an HP Pavilion 6640C with Windows 2000 which I recieved wiped with a clean installation of Windows XP and Microsoft Office 2003. I have tried many methods, such as cleaning up the free space in my system (using Window Washer to remove all traces of deleted data) and Downgrading my Operating System. The reduction in speed makes it impossible to view videos unless they are stored on my hard drive, play basically any game, or use high-resource Java applications such as RuneScape (even in Safe Mode, 250mHZ processor, 64MB RAM rqd). I am running an AMD K6 processor, 256 MB of RAM and a SiS onboard graphical chipset. I can post a hijack this log if required. All help will be appreciated.