If your computer takes a long time to become useable after starting up or logging on, or you want a clean boot of Winodws xp try this,

Click Start > Run > Type "msconfig" > On the Startup tab click Disable Alland on the Services tab check the Hide All Microsoft Service box and then click Disable All. Click Restart and win xp will restart with only the system services and applications running resulting in a vey fast logon / startup.

N.B This tweak will disable all non-system startup sevices and applications so if you have anything you want to run in the background such as anti virus software do not disable that item.