Vista - Very slow network speed

Hello everyone. I have a new PC running Vista home premium 64bit. I'm having problems transferring data across the network from this PC to a Netgear Ready NAS.

Other PC's on my network are fine, but the Vista machine starts the upload at around 50k and then the speed drops to about 10k before it gives up altogether.

The Vista PC is connected by cable to a Belkin Vision router with a gigabit switch. This is then connected by cable to the NAS. All other computers are wireless. The vista machine has a Nvida 10/100/1000 card, I also tried a Belkin USB wireless adapter.

I have tried the following without success -
uninstalling McAfee antivirus
turning off the windows firewall
disabling auto tuning in networking
installing a wireless network card to see if it's a problem with my network card
swapping my router for a different model
changing various drivers


None of this makes any difference.

As other computers work fine I am presuming my network is fine and the problem is with the Vista machine.