Sorry got distracted (Dr Who was on and I'm preparing for a rather long trek tomorrow in the Defender:)).
Windows Live Messenger is a better alternative than the Windows Messenger or MSN Messenger, and will also work XP to Vista and visa-verca. You are best supporting any system from Vista though as it works much better from your end than XP does. From the client (XP) end there's no change.
If they're getting a Vista PC all you need to do is talk them through signing on to windows messenger in Vista. What I'd recommend is setting up a hotmail account for them yourself and then tell them the username and password.
There's also this nice piece of middle eastern software that you can run for them that wipes all the ad's and other junk out of Messenger. http://apatch.ikhost.com/downloads.php
If you need more info let me know. I won't be around the PC until lat tomorrow evening though.

