What are the properties of the VPN client?
Try some debugs on the pix when you try to connect and see what happens, more likely its a configuration issue.
For example, with Cisco VPN's you can allow IPSEC over NAT or disallow it. Though with your Netgear you would have had issues if that were the case.
Use the PDM for the PIX and see if there is something you are missing. By default all traffic is allowed outbound but none inbound so see what sort of authentication the Nortel (Contivity?) requires.
Good luck,
-ne1secure?