Hex-Rays has released a beta of the upcoming version 5.4 of IDA. I was lucky enough to be allowed for the beta-test and the first new thing I noticed was that the command line field now had a button in front of it that says
IDC. This button will allow you to switch between the different command interpreters. Python is now available out of the box along with IDC – almost out of the box.
I have a Vista x64 Ultimate with SP1 installed and Python 2.5 from ActiveState (called “ActivePython”) was installed on my system. However, it was the x64 version that was installed. Also once I had figured this out, it turned out that the installers (x86 vs. x64 are mutually exclusive). The x64 of ActivePython does not come with the 32bit python25.dll, for obvious reasons, but this is what IDA was looking for. The fix is easy enough: install the x86 instead and WOW64 will care for the rest.
Update #1: the Bochs debugger will also take commands through the command line field mentioned above. Cool!
Update #2: Ilfak asked me to try it with only python25.dll available and indeed more than just this DLL is required for the Python command line functionality. Too bad, but it was expected on the other hand.