... dann muss in der Konsole des/der 2008er Server folgendes ausgeführt werden:

netsh interface tcp set global autotuninglevel=restricted

(By default, Vista in normal auto tuning level will use RWIN size of 256 bytes with a scale factor of 8. This value is not suitable for all routers and servers which does not support TCP scale factor, and continue to communicate with 65536 bytes)

Weitere Infos dazu gibt es hier.