Outlook 2003 Not Connecting Over VPN with Windows 7

Just set up a Windows 7 notebook with OUtlook 2003 connecting to Exchange
2003. All current service packs are installed.

When the notebookd is connected locally, outlook connects to exchange and
works perfectly.

When I connect through a VPN tunnel I can browse any shares on the same
server that exchange is on, but Outlook cannot connect. The same account
works fine on an XP machine. A VPN tunnel is the only option for connecting
with this machine when it is outside the company.

Any suggestions for fixing?

Thanks