Ah, I didn't realise that the printer previously worked shared on the homegroup - my thoughts were that you were trying to get it to work from scratch. So, in cases like this, what has changed to cause it to cease to work ? - can you think of anything you may have done e.g. install software, change router settings, change firewall etc.
This is what I would be thinking about instead of believing it is a Windows 7 or printer problem.... let me know if you can come up with anything that may influence the working of the printer.