I've been having some troubles Moving and Deleting large files using Windows Vista, which is apparently a problem that a lot of people are having. I've been searching for a fix to this issue for a looong time now and it looks like I've found it here.
It looks like cause of the problem (at least my problem, from what I've read there are several) is due to Vista's new Auto-Tuning Network. To fix the problem, open up a command prompt as administrator and type in:
netsh int tcp set global autotuninglevel=disabled
...and reboot. After running this fix I deleted a 208 MB file in about 0.5 seconds (which I had previously left deleting overnight only to end up cancelling it) so I think it's safe to say my problem is fixed.
I suppose my network is no longer auto-tuned but what do you expect? Vista to work?