Hi tMrz
Have a look at the Microsoft take on Internet Connection Sharing see
Link Removed -for Vista
Link Removed - forXP
If you get no joy from this, there is a work- round that can solve the problem in some cases. You might need to seek help to try.
Networking different windows versions is very tricky
Each OS adopts a slightly different method to networking; especially with the automation.
The only real way to ensure that everything works fine, is to manually configure each setting to ensure that the OS doesn't assign anything automatically, which is usually where the problem resides.
Follow this procedure to manually configure your network:
1.] View Network Connections
2.] Select the LAN network connection...