more ram needed. forget the graphics card opinion.
xp uses alot of your 256 up, now youve also got whatever programs you use in the background & whatever programs you have open & using.
Like mine i have AV & firewall which start up automatically now that uses extra ram without me actually seeing them anywhere (barring system tray icons)
get anotrher stick, check what progs are running in background.
edit - oh yea run a disc cleanup thing as well get rid of temps etc & spyware scans.