1. How much RAM do you have?
2. Have you gone to Windows Update and downloaded SP1a and all the other Updates that are necessary with a brand new computer?
Open IE > Tools > Windows Update
3. Did the problem just start recently? (try using System Restore)
"HOW TO: Restore the Operating System to a Previous State in Windows XP"
http://support.microsoft.com/default...b;EN-US;306084