I have the only wireless N router in my neighborhood (at least from what I can see), so I don't think there are any conflicts.
I would try this:
1. Default router.
2. Disable ALL optional functionality (even Daylight Savings Time - one of my problems).
3. Enable only what is needed for 300 Mps (see sticky).
4. Verify your router time is set correctly (do not use servers - another problem of mine).
5. Save these settings (for the hell of it).
6. Power down router, power up. Correct the time again (lost on power down).
See what happens.
Mine has been set up like this for over a month now with no problems. I don't use the special functionality, so its no big deal for me.
Also, I have a laptop that runs both XP ans Vista64, and 2 desktops with XP.
I use Symantec Corp A/V.