Autotuning! That's the other one I couldn't think of earlier. This happens either wired or wireless. Firmware, autotuning and the famed Broadcast Flag fix are the 3 main fixes to get Vista working with older hardware.

Like I said before, sometimes none of these fixes will work especially if the latest firmware update is 2004 or some crap like that. A new router is sometimes inevitable. I'm sure Windows 7 will be the same way.