Thank you for your report. I would like to collect some additional information to help track down the issue you have reported.
Please confirm the driver and driver version for Windows 7 that you are using? Is your driver e1k62x64.sys? Is the version 126.96.36.199, dated 09/29/2010?
Are you seeing the errors on the 32-bit, 64-bit, or both versions of Windows 7?
Are you using all default settings for Windows TCP/IP and for Network Connection? If no, what changes have you made?
Are you seeing errors with IPv4, IPv6, or both?
First thank you for your fast reply. I'm using the 188.8.131.52 dated 09/29/2010 drivers on Windows 7 x64. As I said, I can't test on a x86 version of Windows 7 because I don't have any laptop or desktop with a 82577LM network adapter under this version.
I'm using all defaut settings for Windows TCP/IP and Network Connection. I've tried on my laptop, on which I maybe made changes, but I've tried on a fresh installed Dell E6510 Laptop and the problem is the same.
I can't try with IPv6 so i'm seeing errors with IPv4.
I've tried earlier drivers and this doesn't solve my problem.
Thank you a lot !
Disabling TCP/IP offloads will put more load on your CPU. I did not see what Wireshark checksum errors you were seeing, but I am guessing these were probably not real errors. The thread at http://ask.wireshark.org/questions/634/acc-to-wireshark-999-of-my-outgoing-packets-have-a-bad-checksum has good information.
Nevertheless, enabling TCP/IP offloads gave you reduced performance in comparison to Ubuntu. I suspect that the performance issues might be able to be resolved with some network tuning in Windows. I found a number of possible tweaks listed at http://www.speedguide.net/articles/windows-7-vista-2008-tweaks-2574. I have not experimented with these myself, but some of these tweaks might help you.
I hope this helps.