Vista - Transfer to XBox360 very slow

Son installed the 32 bit Vista as a trial and could transfer to his Xbox360 fine, Xbox showing 9 on the transfer bar. He then decided to go 64 bit so I've got the 32 bit now(!). Since going to the 64 bit version, the transfers have slowed right down and are pretty much useless - Xbox shows 1-2 on the transfer bar. All drivers have been updated and he can access the web and download in excess of 200Kb so I'm guessing his network is fine. Any ideas as to why the transfers would slow down so much between the different OS's ??

TIA