transfert rate trouble with 3com 3cr990-tx-97 nic

Hello,
I have a 3com 3CR990-TX-97 nic, under a computer running Windows XP, when doing an upload FTP transfert to another computer of my local area network, the upload runnig at 2 to 5 Mega-Bytes max. The nics of the lan are all 10/100tx.
I have tried with an other nic, a 3com 905c-TX, the bandwith was fully used (at 9 to 11.5Mega-bytes). I don't understand it seem to me that the 3com 3CR990-TX-97 was better than a 3C905C-TX.
I have tried an other test, in a server runnig under Windows 2000 advanced server with 2 nics (a 3CR990-TX-97 and 3C980 TX server) when tranfering data from the windows XP computer with a 3CR990-TX-97 to the same of the windows 2000 server, the rate tranfert was veru lower of 2 to 6.5 Mega-Bytes max.
Then I have transfert some data (under ftp server) from the 3CR990 of the windows 2000 server to the XP computer, the problem was the same, but when using the second nic the 3c980 (of the window 2000 server )to the 3CR990 of the XP computer the rate transfert was seemly (9 to 11.5 mega-bytes).

What should I do to resolve this problem?
Or does it seems that my two 3CR990-TX97 are defectives?

I have ever tried this setting but nothing was happened.