Network and Apple TV problem

Hi Experts,

I am in serious need of help as I have pulled all my hair out.  I have an Apple TV, PC with XP and DI 624 airplus extreme wireless router and cannot make apple TV appear in my Itunes. Apple TV is fine as I took it to an apple shpo and they tested it. My PC is connected to the router via ethernet, all good, a wireless network is established which Apple TV finds and this allows me to get youtube, Itunes store etc. however I just cannot get Apple TV to appear in Itunes. I know the problem is how I set up the network and file sharing. I have opened the ports for Apple TV, been through all their help pages but just cannot figure it out. Some time ago it did work, but I had to rebuild my PC and have not been able to get things working again. Please help.