streaming problems from windows home server

I built a server to store all my movies/tv shows on and am running windows home server. I can copy files from my server to my main computer (running xp sp3), which also runs xbmc, at good speeds (30MB/s). When trying to watch HD movies/tv shows there are times when the picture messes up (hard to explain the problem, looks like giant pixels are showing up on the screen) and the network activity when watching shows/movies spikes up and down. I've attached pics to show you what I'm talking about.

the server is using this mobo http://www.newegg.ca/Product/Produ [...] A785G-UD3H
and my main computer is using a bfg 680i sli mobo

i have them both hooked up to a dir-655 router with cat6 cables.

when copying files
http://img202.imageshack.us/img202 [...] ngfile.jpg

when watching media over xbmc
http://img202.imageshack.us/img202 [...] gmedia.jpg

i know the problem isn't with xbmc since i get the same issue when watching hd movies with vlc...also i know it must be a network problems since watching the same movies locally works fine.

any help would be appreciated