I had 2 PCs on Vista and one on XP. The 2 Vista PCs were networked together and were able to share a printer. I replaced the XP PC with a Win 7 PC. Now the 2 Vista PCs are on separate networks: Network 2 and Network 3. I want to put the Network 2 Vista PC on the other Network 3 Vista PC, to share a printer. I cannot find a way to do this. Thanks for any help.

The Win 7 PC is not on Network 3. It is on a completely different network that is just named Network. Also, the Vista PC's cannot join a Homegroup because they are not running Win 7.