I've had the same problem downloading movies from the iTunes store. It seems any larger files exhibit this symptom.
My iTunes library is on an airport-connected drive (new airport extreme (.11n) with an external HD connected via USB).
I have 80 gigs free, and everything else works fine. I got it to work once by:
1: ejecting the Airport-connected disk
2: turning off Airport on my MacBook Pro
3: re-connecting MacBook Pro to the APort Extreme Base via ethernet cable.
4: (then Airport-connected disk remounted, via ethernet)
I was lucky, and 3 or 4 movies downloaded in under an hour.
Tried replicating that method today - but no luck.
Anyone else having this problem? Digital hub my
*.
Steven
TiBook, Powerbook G4, MacBook Pro, Apple TV, Airport (N, snow, & express), & 2 iPhones.