Paul phones in this link that potentially reveals Joel's intern powered project Aardvark:
XP has this built in with remote assistance, but probably has nat traversal issues. I've used logmein, with mixed results through various firewalls, but they can always fall back to an http, screen capture mode, so you are pretty sure you will be able to get something to work - although slow. I think the pay per use model will probably sell. Although, he he, if your problem is 'can't connect to the network' then, um, game over.