[CKPThunder]

In a nutshell, Bonjour is Apple's service discovery service. One of the services it handles is iTunes home sharing.

First thing I would try is to disable your Windows firewall and see if that works. There are a couple of ports that need to be opened but normally, this is handled seamlessly.

If this doesn't work, then make sure the Bonjour service is running. Use the run command and type 'services.msc'. You will see a list of services that your machine has and make sure that the status of Bonjour is 'started' or something like that. If it's not, then start that service.

If this doesn't work, then go to the Programs under control panel and try repairing Bonjour.

Last resort with Bonjour, remove and reinstall.

EDIT: Wow, just googled this and it looks like a lot of people are experiencing the same problems as you are. Most seem to think it all started when they upgraded to iTunes 10.6.1. This must be an intermittent issue as I am also on 10.6.1 and I don't have this problem. If this an iTunes issue, I hope Apple comes up with a patch pretty quick.