Asking your network guy sounds like a plan ;-)

I have some experience setting up PPTP client VPNs powered by Microsoft Threat Management Gateway (formerly ISA Server) and also site to site tunnels using Cisco devices.

Both have required mutiple inbound and outbound rules of one sort or another, to be manually added... and various out of the box parameters to be tweaked... in order to allow various different network services to work properly.

Obviously you have to be very careful, if adding firewall rules, that you don't accidentally open up your internal network to intruders...