I'm pretty sure the server OS's (such as 2k server and 2003) don't have this limit but I currently have XP installed on this box.
I noticed that every time a second connection was made an error was generated in the event log, but again, not sure if this could be avoided somewhere else.
"The following error occurred in the Point to Point Protocol module on port: VPN5-1, UserName: SOMETHING\SOMETHINGELSE. Because another connection of your type is in use, the incoming connection cannot accept your connection request."
Any suggestions, or should I just upgrade to 2003 sometime?