Is your Display setting is 32 bit or 16 bit ? tell me the resolution 800 × 600 is fit for normal.

http://tech.yahoo.com/gd/windows-xp-display-setting-headaches-everything-on-my-desktop-is-too-small-or-too-big-/3056

www.enableireland.ie/at/pdfs/XP-Display-Properties.pdf

http://support.microsoft.com/kb/309019