both the Mac and the Vista machine are set to acquire an IP address automatically. (DHCP)

While you are at it, take a look at the routers configuration page, see the manual for how to get there, and make sure that the router is set to push out IP addresses.

While it should not cause the BSOD, having two machines with the same IP address, on the same network, will cause one of them to disable it's network card.

Most routers have 4 ports, try using two different ones and check the result.

What happens if the Mac is there first and then you plug the Vista box in? Still get a crash?

You certainly do not need a separate internet service for your Mac. Winboxes and Macs exist on the same network without any problems whatsoever.

Let us know how you get on.