Is there a minimum requirement for VPN?

I have some users who wish to work from home using VPN. I have no problem with this, but I was wondering if there home machines should have to meet a certain requirement. I have come up with a list of things I think they should have, but am also looking for others opinions. Must have: XP Professional or better, broadband connection, and up to date virus protection (must be enabled). Is there anything else the home user should have on there machine, hardware wise?
Thanks