Does anyone know how to tell which RDP version windows is running with?
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The following are the default versions shipped. You can install newer clients (like RDP 7.0 in Windows XP SP3) so it would be dependent on your environment as to whether these have been installed. I presume they would show up as updates in Add/Remove programs.
When you have the RDP window open, left click on the top left corner. In the menu that opens, click "About".