I have a successful RDP connection on Windows XP Professional to Windows Server 2003 at a remote site. I setup another machine running Windows 7 Ultimate. although I am able to get connection, comparing the machines side by side, the Windows 7 connection is dog slow. I have compares that the 2 RDP connections is identical as far as experience etc. I have run a internet connection speed test which show the 2 computers connect at the same speed to the internet.
Remote Desktop on Windows 7 is leveraging a feature called auto-tuning for TCP/IP. This might be the culprit in your case.
I have had success running the following command to speed things up:
Silly point to make, but check whether a cabled connection to your network makes a difference to your RDP client's performance.
I have a Windows 7 64-bit box acting as a server, RDP enabled, etc. Windows XP machines can connect at normal frame-rates over wifi but Windows 7 machines connect at about 1 frame in 10 seconds...
Connecting the Win7 machines directly to my router with a network cable completely cured the issue, so now it seems I have some troubleshooting to do on my wifi network :-)