Virtual PC cannot access internet via host pc with AIS firewall running

Just trying out trial version of avast IS on my virtual PC and can still connect to net. Liked the look of the software so removed avast 4 and zonealarm on my host PC and installed ais. now virtual PC wont connect to the net unless firewall on the host PC is disabled.
Both host and virtual are running xp, set up virtual PC in app rules and tried everything i can think of!! Annoyingly with firewall enabled i can ping my host machine from VPC and share hard disks both ways but cannot get on the net!?!?!? Please guys what am i missing?? is it some glitch?? is there a work around??
Thanks in advance
Xavior