… you’ll probably can solve this problem by activating your integrated Firewall.
It seems that Vista just like Windows XP SP2 enforces the same stupid so called “worm restricting measure”. To make it short: If you disabled the integrated Windows Vista Firewall you’ll have a connection limit. And you probably will run into this limit resulting in strange network behaviours, dropping VPN connections and so on.
Beside activating the integrated Windows Firewall you can disable the TCP/IP “Autotuning” feature:
Click on the Start menu and type cmd in the search box. Type CTR+SHIFT+ENTER to tell the command prompt to open with elevated privileges.
In the command prompt window, type netsh int tcp set global autotuninglevel=disable and hit Enter
After getting the OK returned in the command prompt window, restart to activate the change.
Way to go when it comes to networking :-/