Windows & MSN Messenger fail with error messages

I have recently upgrade from a dial up to a wireless DSL connection - The only problem I have encountered is whenever I log-in Windows Messenger fails with an error message immediately and MSN Messenger fails when I either select the Audio/Video Tuning Wiz
ard on the Tools menu or I attempt to start a voice conversation. I understand because of the wireless connection I am behind a NAT and my pc has a different IP address from the wireless router which can prevent Audio conversations - I had a similar probl
em on yahoo messenger but managed to fix it by creating a virtual server on the router for Port 1863. Is there anything else I have to do to enable Voice and stop Windows and MSN messenger failing. I have gone back to a restore point prior to upgrading m
y connection and the Wizard works perfectly so I can only assume it is caused by the upgrade. Any help would be greatly appreciated.
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Duncs