256 MB RAM is not good for XP systems - it is the recommended minimum... Try to get min 512 MB or even 1 GB...
Also, turn off the eyecandy in XP by making it look in classic mode. 1. Right-click desktop and select Properties, go to Themes tab and select Windows Classic... 2. Right-click My Computer and select properties, go to advanced tab and select Settings for Performance, select the option to Adjust for best performance...
Arun