Sharing a printer between windows vista and windows 7?

The printer must be turned on first. Also, the Vista computer must be turned on and logged in every time you need to print, as it is the machine that is providing the printer a network connection to the router. If that is a deal breaker, you can get something called a "print server" that lets you hook the printer directly up to the router, then you can print from any system in your network at any time (as long as the printer is turned on).