vista copying files from wk3 x64

I have a GB network, several machines...wk3 64 bit, winxp x86, vista x86.
copy files from wk3 x64 <-> winxp x86 works great
copy files from winxp x86 <-> vista x86 works great
copy files from wk3 x64 <-> vista - sucks. typically I'll get 24 kB a
second....in a GB world..unacceptable.

I've tried disabling autotuning...remote differential compression...but
there is something wrong here. I've even applied RC of SP1 in hopes of this
fixing this issue...but no.

suggestions please and thankyou.