You can download and install the new, updated RDC 7.0 client for free for any OS from Windows XP SP3 and later (it ships with Windows 7) known issues here and detailed feature comparison per OS here and downloads for various client OS’es are below
Update for Windows Vista, x86-based versions
Update for Windows Vista, x64-based versions
Update for Windows XP, x86-based versions
A nice touch that i discovered by accident is that you can move the top title bar along the top of a full-screen RDP session by clicking and dragging, this is really handy if you work on multiple full screen RDP sessions inside another RDP session – for example a jump-off box to a protected subnet or when you have a full-screen application.
AkA Terminal Services client, Remote Desktop Protocol Client, RDS Client, Remote Desktop Client, RDC, RDP, RDS