My home sharing on itunes is on but can't see it on my apple tv... any one knows why... I checked every thing

What kind of router are you using?

Your router is the problem. Unless you can get it to allow Bonjour traffic, then Apple devices that use the Bonjour service are not going to work. You could look for a fix through eircom support. Or try a different router. Any Apple airport router would absolutely work.

iTunes Home sharing requires mDNS / Bonjour protocol and DAAP to work. Bonjour uses UDP 5353 and DAAP uses TCP 3689. Your router must be configured to allow network boradcasts on these ports.

It will allow your homesharing, airplay, airprint, propreitary apple networking support, and other features. You should absolutely try to enable it. Some routers, even when the ports are opened, just don't work perfectly with Bonjour broadcasts. But you might be able to get it to work. Look to see if anybody else with your router has already figured this out in the eircom forums.