No problem on the delay... I had a couple of busy days too...
Two ideas come to mind...
In your router's wireless settings, make sure that CTS polling is enabled. This is one of those bizarre situations where a router setting can cause an apparent fault in a computer device. Clear To Send polling ensures no packet collisions or overruns (your laptop sending faster than the receiving device can handle). This may slow your wireless down a bit (abt 5%) but if it works, I'm sure you can live with that.
One other thought is that if you are running on batteries during these big transfers, the system may be switching Wireless settings at various battery levels to try to extend battery life... This is a setting in power management. My Toshiba (XP Pro) did that and it was plain enfuriating "Wireless is now connected" messages every time...
On the topic of switching to Win7 Pro... Yes, I do think it would be a good idea. As I mentioned before I had a LOT of issues with Ultimate, so I switched everyone to Pro and it's been a lot better. Look around here, most of the support appeals are for Win7 Ultimate even though Pro is outselling Ultimate.