r8169 + network slow and unstable.

I have two sweex gigabit network cards. They are based on the rtl8169s
realtek network ic.
One of the cards is in my athlon (via chipset) pc (windows xp) and the other
is in my pentium pro 200 (asus)
pc (linux 2.6.0-test11). I am testing the stuff with a 3com switching hub
and a sweex switch.

The problem is that the network speed is very slow, about 1,3MB/s. Further
more the connection is
very unstable. Most of the times it suddenly stalls and stops working
completely. Only some ping
icmp packets from my linux (ppro 200) pc to the windows pc can revive the
connection.

Some other strange thing is that ftp transfers to the ppro pc goes fast, but
ftp transfers from the ppro pc goes slow and stalls; this is certainly the
case when i transfer large files. My switch and hub are both indicating good
network conditions -> no collisions and both 100MB full duplex.

I tried linux on both pc -> no luck.
I tried replacing my hub with a switch -> no luck
I tried kernel 2.4.22 and 2.6.0-test10 and 2.6.0-test11 -> no luck

Maybe someone can help me out here.

Thanks!