tony draper,
The only thing I know about XP is I do not like it, it seems to take forever to boot up or shut down and it is always accessing his hard disc,
That computer is not configured correctly and might be short on RAM. That would explain the lagging performance. With WinXP you really want to use 512Mb of RAM.
If you are still having problems getting MSBlaster out of that computer, hit CTRL+ALT+DEL and go in to the Task Manager. In there look for MSBlast.exe and hit End Process.
That will stop the countdown and let you remove the worm from the computer.
Take Care,
Richard