For anyone who needs to access their intranet via ipsec, Parallels Desktop 4.0 now works correctly. Previously I had to setup ipsec for the Mac OS side, and then when running a Windows XP VM, use the Windows VPN(l2TP) "dial-up" connection for the VM to access the same addresses. Now a single ipsec or Mac OS VPN connection should allow you to access your company intranet. My OS X system is setup for a host-to-network ipsec connection to the company firewall using ipsecuritas. The Parallels VM is configured for shared-networking. Applications in the VM can now access intranet side addresses - the only special change I had to make was to explicitly add the intranet DNS server address and DNS suffixes to the Windows network interface settings.
