RDP is Microsoft's attempt to add to Windows a feature that has been built into Unix for YEARS now. Most of your Unix boxes use a protocol called X-Windows. On your PC, you need to get an X-Windows server, such has "Hummingbird eXceed".
If by "enable" you mean that you want to, on your AIX machine, bring up a windows desktop via RDP, then you'll want to look at the program "rdesktop" (check out
http://www.sourceforge.net/ for the source code, etc.). rdesktop is an X-Windows program that speaks RDP to a PC and brings up a Windows desktop on that PC in a window on your X-Windows desktop.
I don't know of any program that would say take X-Windows calls and translate them into the equivalent RDP calls. Your best bet would be to look into rdesktop, perhaps there are some forums for rdesktop that you could ask around in?