I can ONLY RDP to Windows Server 2008 from XP workstation.

• Log on as an administrator to the remote 2008 server by using the console or by using Remote Desktop Services FROM A Windows XP CLIENT.
• Open an elevated Command Prompt window (shift-right-click on the Command Prompt icon and select Run As Administrator, or type CMD in a run box and press ctrl-shift-Enter).
• At the command prompt, type the following command, and then press ENTER:
                 winrm quickconfig
• Answer Y to any prompts and then disconnect the remote session by closing the window (note: You do NOT have to restart the remote server).
• You should now be able to connect to the remote server from the Windows 7 client, although it will appear to take longer than it does in XP, so be patient.

Incidentally, this same fix can be used on a Windows 7 desktop PC to fix a problem where a Windows 2003 RDP connection from a Citrix server cannot connect to the Windows 7 system even though you have enabled legacy RDP client connections in both the System Properties ->Advanced System Properties -> Remote settings AND in the Local Group Policy editor (gpedit.msc).  

Source:
http://social.technet.microsoft.com/Forums/en/w7itpronetworking/thread/f0229ab4-336b-4d63-832d-e71f51002645

All computers are on the same physical network. No firewalls. Local firewall on the Server 2008 machine is disabled.

Machine is reachable by RDP from any of the XP computers on the network, but from none of the Windows 7 pc's or any of the other servers.

Thank you for your response, nimatejic. I've tried your solution. In the past, and again today. No luck.

When trying to RDP from Windows 7, what error message do you get.
Any error message in event viewer on the Server or on Windows 7 machine?

Nothing in the Event Viewer. On both machines.

I've also done a compare of the registry with a working server and couldn't find any differences in the key "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server" Are there other registry keys that I should check out?

What message do you get when trying to connect?

This computer can't connect to the remote computer.

Try connecting again. If the problem continues, contact the owner of the remote computer or your network administrator.

Can you access shares on the server using UNC path?
Can you ping the server from Windows 7 machine?

Yes, I can access shares and ping to the server.

Something else has happened now. I have gone into Terminal Server Configuration and changed the network adapter. Since then I cannot access the server from XP either... I have changed the configuration back to what it was, but still no luck. I get an authentication error - haven't googled it yet, but will do...

Thank you for your help thus far. You may rest for a while :-) I'll come back to you in an hour or two...

Please also check the RDP session security. Do you have rights to connect?

This is really driving me mad now. I've read somewhere that I should add "enablecredsspsupport:i:0" to the RDP file, to solve the authentication error. I've done that, now I get the same error on the XP machine as I did on Windows 7.

I've added the string on my Windows 7 pc. Guess what, I now get the authentication error on my Windows 7 pc! (Code: 0x80090330)

Have you tried this?

Logon to the server locally
Click Start, Run, type "tscc.msc /s" (without quotation marks) and click OK
In the Terminal Services Configuration snap-in double-click Connections, then RDP-Tcp in the right pane
Click the Network Adapter tab, select the correct network adapter and click OK
Make sure that you can establish an RDP connection to the server
The change takes effect immediately. No need for a restart.

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