Windows 7 avi files not visible on network

[roscored1000]

I am pulling my hair out trying to get a few things sorted out with my home setup. I have media pc running windows 7 ultimate. But trying to stream AVI files over Cat6 cable to my local network to my media player [zensonic/ziova z500] just doesnt work, I can see the folders but not the contents,using UPNP, the only files visible are WMV MPEG. Its driving me nuts because I have installed Vmware and XP sp3 and by copying some of these avi files to the xp shared folders I can see them all immediately, where is windows 7 different. I have set up folders to share on the w7 network but no luck, any help appreciated.
Funnily enough I can see AVI files on the network from my Vista laptop, not sure what is different?. thanks