Aaand finally, the circle is complete.
I downloaded the fpc, fpc sources and lazarus packages (.deb) from Sourceforge, I installed them in the usual order (fpc, src, lazarus), started Lazarus, it complained about gdb missing, installed that too (apt-get install gdb), and Lazarus 1.6.2 started with no further complaints.
Unfortunately, I wasn't able to compile the empty application, nor the IDE. The error message looks familiar:
lazarus.pp(53,3) Fatal: Cannot find interfaces used by Lazarus, incompatible ppu=/usr/share/..../gtk2/interfaces.ppu, package LCL.
This thing is, on Linux, as broken as a broken thing can be.
Armin.