Try entering the ip address of the Windows Vista Computer instead of the computer name. There may be a problem with translating the name into an ip address.
Also you say the two computers are on the same local network but could you supply more details. I mean are they both contacting a wireless hub to get their ip address or are they both plugged into a wired ethernet hub? Is one wired and one wireless, etc? Do the laptops have fixed ip addresses?
It is possible that the two computers are on the same network but are being supplied ip address within a different range.
Yes they are connected to the same Netgear router which is wireless. Both computers are wireless.
Also, to get the ip, do I just type ipconfig in the cmd and then get the default gateway? Or is it something else. The ipconfig thing didn't work.
Also, I have filesharing on and SMB on in my MBP, and filesharing is on in the XPS laptop. But I still can't see it in my "Shared" de vices in the Finder. Maybe that is the whole problem?