Yes, I've apparently done something wrong. It might be as simple as "something's in the wrong place". But if everything looks reasonable, it must be something invisible like the partitioning or formatting.The problem you had when in the script menu is caused by CHDK not being able to find the FSELECT.FLT file in the MODULES directory.
Weird, it's there. Oh well, time for try #2.
Does this look like the right file? I downloaded it from http://mighty-hoernsche.de
(CHDK-SVN Autobuild Download) a few days ago.
-rw-rw-r-- 1 eben eben 666982 Aug 1 18:39 sx1-201a-1.2.0-2999-full_BETA.zip
eben@pc:~/torrent/chdk$ unzip -l sx1-201a-1.2.0-2999-full_BETA.zip
1919970 211 files
Incidentally, when CHDK boots do you see the round CHDK icon (like the one on the top of the wiki page) or just the text box with filename and data info?
Solid red box with white text:
CHDK version ''CHDK 1.2.0 -2999-0'
Build : Aug 1 2013 22:54:22
Camera: sx1 - 201a
I had to restart the camera a bunch of times to transcribe that, so I might have missed something.