Finally ...

I found this thread like 3 hrs ago..., I followed your advises and thank you all, but there was still one step left for me...

I had installed aMSN, and as a dependency it installed Tcl/Tk 8.5, but only the binaries, not the dev packages...

The python installer was confused, thinking that I had installed the 8.5 dev packages (given that I had the 8.5 binaries), and was looking in the right directories...