I think Differential Compression could be the reason why it's so slow for you. Try turning it off and seem if it's any better for you.

* Configuration -> Programs (or something of the sort... I'm using a Dutch version)
* en/disabling windows parts
* look for "Remote Differential Compression" and remove the check
* reboot.

Lots of people have reported Vista being dog slow at copying. This tweak is said to fix it.