Hello there,
If all your other drivers installed fine than all you have to do is seek out the lan driver for your motherboard.. This could be done offline if you have the driver disc that should have came with your mobo when you bought it...
If you can get to another computer with online capabilities (which I assume you can since you wrote this message AFTER installing Win 7) than search for the latest Windows Vista driver for your motherboard and install that.. it SHOULD work.. if not than try messing around with compatibility mode and see if you can get it running that way.. if none of this advice helps, let me know and we'll try something else..