Ok, hold your horses here. This morning I turned on the computer, opened iTunes, and Home Sharing was gone again, as well as my Apple TV 1st Gen. So I figured it was something that reset when cycling the computer, and that the desintallation of iTunes 11 and resintallation of iTunes 10 reset, but then when cycling the computer it went to its previous state.
So I started testing Windows Firewall settings, and realized that going to Firewall with Advance Settings, clicking Windows Firewall Properties, Inbound connections on the Domain Tab drop down menu, "Allow" (from block (default)) made Home Sharing to start again and my Apple TV 1st Gen to show up again.Crazy (modifying the other two profiles, Private and Public had no effect whatsoever). So thinking this was probably a Bonjour issue with Windows Firewall, I clicked on all Bonjour Service lines on the Inbound Rules of Windows Firewall and made Bonjour allowed on all Profiles (Properties/ Advance/ click on each profile at the top for a check mark). Clicked apply
Closed iTunes and reopened, it worked. Restarted the computer, Home Sharing came back, as well as my Apple TV. So it seems it is a Windows Firewall issue more than and iTunes 11 or any iTunes issues. Try and let me know
This page is also useful for TBshooting WFirewall issues
http://www.tech-recipes.com/rx/18359/troubleshooting-itunes-wi-fi-sync-problems- in-windows/