Slow Network Performance With Media Centre

I have an 10/100 wired connection through a linksys router to an XBOX 360 and am running Windows Vista Home Premium SP1. I've had ZERO succuss in playing MCE content - ie MP3s and viewing JPGs - on the XBox.

The Media Center menus on the Xbox are intolerably slow, taking 5-30 seconds to respond. Eventually if I have the patience to wait until the XBOX Media center accesses the files located on the Vista machine it takes upwards of 2 minutes just to load one jpg. When I run the tune network tool in WMC I get a message saying that:

"Your network may not have enough bandwidth for consistent performance on your extender device."

When I view the performance graph in the tool my bandwith barely registers on the graph.

Other things I have tried to no avail:
- turned off all firewalls
- unitstalled anti-virus software
- port forwarded the following ports in the router, TCP2869, TCP10243,
UDP1900, UDP10280 to UDP10284
- played with the flow control settings
- tried selecting all possible "speed & duplex" settings

Support from Microsoft sucks:mad:. The XBox people have pawned me off on the Vista support people. I wouldn't let the Vista support people hand me back to the XBox people...although they tried pretty hard. The Vista support people are saying they need to recreate the problem in their lab and get back to me.