Windows Vista, VPN - Network Shares & Outlook 2003 Connectivity is

Our first Vista based machine on our WAN network is giving me grief.
Basically it will not connect in Outlook 2003 and is unable to view other
computers on the network or access network shares.

The machine is running Vista Business 64bit and is connecting to Server 2003
(sp1) & Exchange 2003 (sp2) via a hardware VPN. We have tried it on multiple
VPN connections with the same result, however the XP machines at both sites
work perfectly!

On the Vista machine I can ping the servers' IPs, Netbios name and FQDN OK.

I have tried:
-turning off windows firewall
-disabling and uninstalling mcafee security centre
-enabling netbios over tcp/ip
-disabling ipv6 on connection and in registry
-manually entering DNS, WINS servers
-tried connecting outlook using https
-tried RPC registry entry in KB899148
-tried lots of changes on the router (firewall off, NAT off, uPnP, etc)

When I take the VPN out of the equation (connect to the LAN) the PC works
fine. The VPNs are based around a Cisco ASA & linksys routers.

Any help would be greatly appreciated! I'm out of ideas...