Time Machine Problem with Network Drive on Vista Machine

So I have been having an annoying problem. I have a macbook pro and a Vista desktop. I had set up time machine so that it had been backing up to a drive on my vista machine (and it was working fine). I recently replaced the hard drive in my macbook pro and now time machine wont work. I get a failed message when I try to back up to the networked drive saying that the backup disk image could not be created. Now I don't recall exactly when backups stopped working so it is possible that they stopped when I upgraded to leopard 10.5.2, but I'm really not sure. So does anyone have any ideas or suggestions? Am I missing something to write to NTFS drives or something? I seem to be able to transfer files just fine from finder. I'm really rather stumped by this and also a bit annoyed. So any ideas?