DOS and NIC set at 100 Full Duplex

Hi,
I'm making a network connection through MSDOS 6.22 (using normal network boot disk, IP via DHCP) on a workstation with a 3Com 3C905C-TX 10/100 card. This workstation is dual boot to XP. Both XP and DOS have latest NIC drivers.
The card is set at auto negotiate, as is the port on the switch (I believe a Cisco 3500).
There is a Windows 2000 server on the same switch, forced at 100 Full Duplex (both server and port).
Now, the 3Com card auto negotiates to 100 Full Duplex both in Dos and XP. Copying large files between the server and the workstation while in XP is fine, though a little slower (some 2000 frames per second slower) when copying from the client to the server as opposed to the server to the client.
However, when you boot into dos, copying from server to client is reasonable (slower than XP, but acceptable), but copying from client to server is very slow (bounces between 4 to 300ish frames per second), taking many minutes to copy just a 70Mb file.
Is there a known issue with running a network card at 100 Full Duplex while in DOS? Does it need to run at 10 Half? We have tried it at 10 Half, but found the port had also to be forced at 10 Half for it to work reasonably - no good while in XP.
Many thanks for any help,
P