Vista - Windows Vista NAT Issues

I have been running an XP Pro version of windows over an internal network
that uses Cisco Switches and Firewall (private not corporate) and Network
Address Translation in order to securely go out into the internet.

In addition, Remote Desktop has been working just fine back to the office
via terminal server.

I have recently upgraded to Windows Vista business addition and there are no
issues with general internet access at all, nor with normal downloading of
information. I did a test of loading a 12meg Tacac router config from Cisco
and it downloaded with great ease and speed. I was happy during those tests
:-)

However, I am stuck with a small issue that my Remote Desktop functionality
is is having issues now I am on Vista. It attempts to establish a connection,
but then gives the impression that it freezes. Running a wireshark capture
session, it looks like there is a forced reset of the packets, but I can't
work out why! I am less happy at this point ;-)

Doing an isolated test, I eliminated my internal Network as I suspected it
was a NAT issue, and so I bypassed everything and plugged my Windows Vista
box directly into the Internet connection. This solved the issue instantly,
which to me indicates that somehow Windows Vista processes any form of NAT
event differently to Windows XP. I am now excited that there is an issue to
overcome :-)

I've tried looking at all the Network Settings within the Vista environment,
but decided at 3am this morning after scratching my head that I would post on
here.

Have you ever encountered this before, and if so, could you provide me with
a direction to go in.

Many thanks chaps.
Paul.