The messenger service has been disabled since SP2 in Windows XP. It won't work unless you flag it as at least "manual" and start the service - it needs to be enabled on the recipient computer.
*EDIT*
And that is in the services MMC, if that seemed confusing. Go to run and write:
Code:
Find the messenger service, and you know what I'm talking about.
*EDIT*
And that is in the services MMC, if that seemed confusing. Go to run and write:
Code:
Code:
services.msc