You need to network the two computers (If you haven't already done so) and ensure that both are using the same network name. If I remember correctly the default for Vista is MSHOME but Win 7 is WORKGROUP. It doesn`t matter what the actual network name is as long as they are the same.
Another common pitfall is that on both computers all Users should have a password set up to log in with.
Thirdly, set the printer up with the correct drivers to print by USB direct to the Printer. This ensures that the drivers are held locally on the Vista laptop. Then revert to setting up the connection via the network.
Post back if you run into problems with any stage.