I'm trying to stream both 720p and 1080p content to my 360. When trying to stream something, like the Tron Legacy trailer, the video stops every 30-60 seconds before starting again. I'm running a wired, gigabit network, and I'm running Windows 2000 (service pack 1) and have a p4 3.0 gig with 2 gigs of RAM, and am using the on-board NIC for an Asus P4c800 deluxe motherboard. I haven't had any issues streaming to my PS3, and I want both of them to stream well. I'm using PS3 media server to stream the content.

Can anyone offer any advice on what I can do to improved streaming, without being stuck at 480i/480p resolutions?

You may have a flow control issue due to the difference between the Xbox 360 network speed and the gigabit speed of the router. You probably want to go into the advanced properties of the NIC (on the PC) and see if there are any settings you can change related to flow control.