This will update Windows Messenger to version 4.5 Notice earlier I suggested NOT installing v4.6 from Windows update. the reason is because of an MS bug. If you install v 4.6 BEFORE you set up other WIndows XP user accounts, then only the administrative user will be able to fully use Windows Messenger. Therefore by clicking the link above you will get v4.5 which is where you want to start.
Once v4.5 from the above link is installed, reboot
Now youre ready to set up any additional Windows User accounts you want. Logging onto the internet while in Administrator Mode can put you at higher risk of vulnerability. So consider setting up a Limited User or better yet, Power User account for yourself
Once the User Accounts are set up now you should try logging into Windows Messenger for each user account.
Once youve done this - now log into Windows as an Administrator and go get the most recent Windows XP Messenger update.