Ok, new update:
i downloaded firmware 100e and ported chdk to it. This is completely untested since i only own a 101a (not for long..as i said in the first post) but i checked briefly the diff against another 100d and it was pretty small so it *shouldn't* cause issues.
Meanwhile i checked out some raw addresses, fixed some defines (i'm not into the raw field so they might be wrong) and updated code a bit.
You can find the source code at the usual address: https://github.com/c10ud/CHDK/tree/s100
I think i will generate a diff and ask for inclusion in the chdk svn trunk soon so a wider audience can be reached and obvious bugs can be better identified and fixed. I wanted to take a look at gps functionalities first but i don't know if i'll have the time.
For those curious/eager to test, here are my local builds for firmware 100d, 100e, 101a.USE AT YOUR OWN RISK