Sensible,
The sweet spot with WinXP is 512Mb of RAM. That will give you the Memory to run 99% of all the programs out there.
With a 550Mhz K7 you really are borderline for running WinXP but workable.
Your motherboard is either a VIA or a SiS Chipset. I would look into getting the latest drivers for your motherboard along with the RAM. That should solve most of your issues.
Take Care,
Richard
P.S. If you would list the specs on your Motherboard, Video Card, and Sound Card, I would be happy to get you a list of drivers to install.