Vista - Vista and XP Home Networking Problems

Hi,
I have a weird problem in my network setup.
I recently upgraded to a Gigabit router since I wanted to install a small file server and wasn't satisfied with 8Mbyte/s on 100Mbit.
Well, my problems is as follows :

Starting transfers on my Vista Ult. SP1 Workstation :
Vista -> XP Home SP3 = 17Mbyte/s
Vista <- XP Home SP3 = 17Mbyte/s

Now the kicker if I start the transfers on my XP Home Server :
XP Home <- Vista = 17Mbyte/s
XP Home -> Vista = 55Mbyte/s !!!!!!

So, if I start the file transfer to my Vista machine on the XP Home via Remote controle I get decent Gigabit speeds but not in any other case.
I tried disabling and enabling :
-Jumbo Packets
-IPv6
-QoS
-Flow Control
-Checksum Offload (any offloads I could turn off I tried)
-Auto-Tuning (tried even different levels of it)
-Tried killing all processes I could on the vista machine
-Tried the fix to disable the Multimedia Class Scheduler

Nothing changes the speed even by a bit...well, enabling Jumbo Packets on the XP Home Machine made everything worse, that was the only thing that made any change at all.
The Physical connection must be ok since I do get 55Mbyte/s one way, so I guess there must be a software problem somewhere.
As it is now I can't do what I wanted, which is treat the server as an intelligent HD so I can, for example, map the server drive and decompress a file directly from there to my local disk with the horsepower of my local machine. To do that now I have to log on remotely to my server, push the files to my local HD and then I can decompress them.
If you wonder why XP Home SP3 is on my server....well, it was on there and it works, Vista is a no go for that machine since the server is not powerful enough for that.

Hope someone has an idea what might be up with this