I've got an odd problem that I'm not really sure where to start the troubleshooting process.
I have a 'server' with Windows Server 2008R2 (64-bit) installed and it has a couple of hard drives. If I Remote Desktop into the server and transfer files from one HD to the other, all it fine.
If however, I use my workstation (Windows 7 64bit) and open up a shared resource on the server and transfer a file from one hard drive on the server to another HD on the server (not using Remote Desktop, just Windows explorer/Network places), the transfer crawls... It takes about 5mins to discover files/calculate the transfer and then starts transferring at speeds like 56KB/s - 200KB/s.
Both machines have Marvel GigE network ports with a TrendNet 8-port green GigE switch. I've set Jumbo packets to 9K on both machines...