For those of you who have ever wondered why you can only terminal in one session at a time for windows XP but you could do it with Windows 2000 and the very first release of Windows xp,  It because windows does not support it, and does not get paid for it.
 
If you think you need to use a Windows XP machine as a terminal server,  here's the unsupported way how to do it.  (In other words, you do this at your own risk!  Don't call me if it doesn't workfor you!)
 
Print these directions so that you have them to work from.  
Restart your computer in Safe Mode  
Turn off/disable Remote Desktop Connection (RDC) and Terminal Services  
Right click My Computer  
Select Properties  
Click on the Remote tab at the top of the window  
UNCHECK the box next to, “Allow users to connect remotely to this computer“  
Click OK  
Go to Start -> Control Panel -> Administrative Tools -> Services  
Find Terminal Services in the list  
Right click on Terminal Services and click Properties  
In the Startup Type box, select Disabled  
Click OK to close the window  
Next you will replace the current version of the Terminal Services DLL (termsrv.dll) with an unrestricted version from a previous release of Terminal Services.  
A copy of the Terminal Services DLL - is at http://chiefgeektek.com/files/termsrv.dll Save it to your Desktop or other suitable location  
Using a file manager like Windows Explorer open C:\Windows\system32\dllcache  
Rename the file termsrv.dll to termsrv_dll.bak or whatever you would like.  
Copy the downloaded termsrv.dll file (the one you just downloaded from the web) to C:\Windows\system32\dllcache  
Open the C:\Windows\system32 folder  
Delete the file termsrv.dll in C:\Windows\system32  
Now we can edit the Windows Registry to enable more than one RDP connection. Go to Start -> Run and type regedit - Hopefully you knew that already  
Go to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\Licensing Core  
Add a DWORD Key named EnableConcurrentSessions and give it a value of 1  
Close the Registry Editor window  
Go to Start -> Run and type gpedit.msc to run the Group Policy Editor  
Browse to Computer Configuration -> Administrative Templates -> Windows Components -> Terminal Services and double click Limit number of connections  
Select the Enabled button and enter the number of connections you would like to enable….at least 2.  
Restart Windows  
Right click My Computer and select Properties.  
Click on the Remote tab at the top of the window  
CHECK the box next to, “Allow users to connect remotely to this computer“  
Click OK  
Go to Start -> Control Panel ->Administrative Tools -> Services. Select Terminal Services from the list and double click it or right-click -> Properties. Set the Startup Type to Manual.  
 
Restart Windows/Computer  
You should be good to go.
 
AGAIN!  This is at your own risk!  Please do this on a test machine!