You can get conditionals and other scripting capabilites with the InnoSetup Extensions available at http://www.wintax.nl/isx/. I use it a tiny bit in the wxPython installer, but I've heard that it can do a whole lot more.
Ya, I looked at that. That's what Python needs: to ship an installer with an embedded Pascal interpreter <wink>.
Wise kindly offered to let PythonLabs use InstallerMaster 8, and I just got the box from UPS today. So my strong bet is that's the future for the PythonLabs Windows installer. All you other suckers are on your own <wink>.
Seriously, I hope *someone* picks up python.iss and finishes an Inno installer for Python, Pascal-driven or not.
BTW, I tried MS's Visual Installer (currently free, no idea whether that will last) MSI authoring tool, and limped away screaming in terror. If that's the future of Windows installer technology, I'm glad I still have a few friends left in the Linux world ...