How to setup multiple incoming VPN on XP Professional machine?

I have Win XP machine with data drive which needed to access from three Clients (Win 7 Home machine - Same time - all day) for their day to day work. What software / hardware I need to setup three incoming VPN connection on this XP box? I know WIn XP Prof can handle only 1 VPN at a time, which is setup on my XP box.|||Easy way - buy VPN router - good one rv042 ($150),you can have up to 50 QuickVPN tunnels for remote client access|||Switch to Linux. If you need to use XP apps, you can install XP in a virtual machine.