Hi,
I'll try and make this as short as possible. But I have a lot of info, so warning, it's long!
All devices have latest updated firmware. All PC's have fresh installs of windows (less than 1 week), with all latest patches.
DIR-655 Xtreme-N router
DNS-323 NAS (2x 500 GB Western Digital 7200 rpm in RAID-1)
Desktop: wired - Windows 7 x64
Laptop: wireless - Windows XP x32 - DWA-652 Xtreme-N
Desktop2: wireless - Windows Vista x64 - PCI DWA-552 Xtreme-N connection
Ok, I just bought the NAS last week. Up until now, my wireless network has been flawless for the past year or so. Awesome range/speed, etc, on both wireless PC's.
I used to use Windows sharing to share a hard drive in my wired PC. I would then play/stream videos (700 MB AVI files) over wireless to the laptop. The problem was, the video would glitch pretty much every 30 seconds on the queue, sound would continue, but video would freeze then catch up a few seconds later.
So I started just copying the file wirelessly to the laptop first, then playing it. Which worked great but was annoying. I guess it was just the overhead of the windows systems each not playing the video perfectly, on top of being wireless. Maybe?
So I bought the NAS to try and solve that. Moved all media to NAS. It works great on wired PC. I used the NAStester 0.4. And after enabling Jumbo Packets on my wired card, got up to 32 MB/s speeds. Satisfied!
Wireless tested - ~5MB/s write/read on both laptop and desktop2
But I can't stream a movie! Same damn thing. Glitchy video, pauses, freezes, crashes VLC and Windows Media Player. Before, with windows sharing and no NAS, it was at least flawless to run the file every time, just glitchy video. Now, with the NAS, it is much worse. 50% of the time it will not play the file at all, or takes up to a minute to run it. Windows Explorer crashes (not responding) for long periods. I have to end task the explorer. I can then still browse the NAS directory, but if I play a video again it crashes. The other 50% of the time it will play, but freezes completely after about 30 seconds or so, and crashes the media player.
This is even whether or not I am 2 feet from the router/NAS. Or across the house. I must stress that before, with Windows Sharing, I could be out in the yard and access any file flawlessly, just glitchy video on movies.
I can stream movies to the wired desktop from NAS just fine.
The internet on wireless is flawless still. I re-enabled windows share to test, still as before.
Here is the other thing. As mentioned before, just plain old browsing the NAS in Windows Explorer crashes it often, not responding explorer, end task, etc. After re-enabling windows share, no issues at all with Windows Explorer, never has been any issues. If I transfer the movie first, it says "2 minutes..", gets to about 75% then crashes, or waits a few minutes with zero progress, then finishes the transfer. Before with windows share, it never did this. The transfer was good, but 3 minutes.
All problems are evident on both laptop and desktop2. And no other PC is accessing the NAS at that time of testing.
I really want to use a NAS, but this one is giving me a headache.
I want to rule out my Network cards, and my router as there were no issues before.
I want to rule out my computer, as there are 3 of them, all with different hardware and operating systems. And the movies play just fine when transferred to the laptop first.
I speak to the IT guys at work and they are like "man, I stream HD movies over a DIR-655", and also one guy said he streams AVI files over an old Wireless-G setup with zero issue.
I mean, you can stream movies over the internet for crying out loud, why is my kickass home network not doing it? Help! I need to solve this before my 30 days to return the NAS has expired

Thanks in advance!
Settings screenshots, note I also have another PC that is my mother in-laws on Wireless-G, hence the mix G/N mode:
NAS : link speed auto
jumbo packets 7000
(I have tried with this off)off = FTP server
off = upnp AV server (I'm just clicking movies in explorer and playing them that way)
off = iTunes server
off = dhcp server
off = LLTD
(I have tried with this off)