I'm putting this in a separate message because it's not really germaine to our troubleshooting... but it might shed some light on your problems.
My home network consists of my HTPC (ASRock ION 330), my homebrew system (AMD X2), my smarter half's system (same as mine), my son's homebrew system (Intel Core i7), a netbook we all use (Aspire One), a "family machine" (same as mine) in the basement that's used mostly for music, and a number of assorted laptops that "guest in" on wireless.
The HTPC is on XP/sp3 as is the Netbook. My son's system is on Ubuntu. The rest are on Win7 Pro.
1) I could not get Win7 to work on the HTPC or Netbook ... even though both are supposedly rated for Win7. The htpc in particular crapped out badly, wouldn't play FLAC or high bitrate MP3 without burbling and was dropping frames like crazy on 1080p. Both work perfectly on XP.
2) The machines that are on Win7 would not work on "Ultimate" but reverting to "Pro" got them more or less working. There are still issues that we can't fix but I've managed some workarounds for the time being.
3) On the Win7 machines the multimedia playback positively sucks. With even moderate bitrate AVI files, video frame dropping is common, motion is jerky and CPU usage is ridiculous... 50% of an X2 (64bit dual core) processor to play a movie... I don't think so.
Looking around the web it becomes apparent that most "Audiophile" and "Videophile" sites are still treating XP as the operating system of choice for multimedia and I'm forced to agree. XP does a far better job of multimedia providing better playback on Atom processors than Win7 does on AMD X2 processors (1.6 vs 2.8 ghz)... The video quality is better. The sound quality is far better. CPU usage is way down...
But for our discussion the netbook is most relevent... I've done 80gb transfers between the netbook and my backup drive (attached to my machine on USB) without a single problem... many times. This is over 802.1 Wirless, probably very much like yours. When I tried Win7 in it... The wireless was pathetic, slow and re-connected constantly.
Now I'm wondering if you aren't in the same boat...
My solution was to revert it back to XP and all is well.
I don't know if I'd recommend that for you, but it might be something to think about.