Well, if I find a page on maemo.org that tells me which libc is installed on the OS2007, I could help. Something like packages.debian.org.

Anyway,

Depends: libc6 (>= 2.5.0-1) but 2.3.5cs2005q3.2-5.osso12 is to be installed

You are not using the scratchbox repository on your device are you? I'm a bit surprised about the version number of libc6 which looks roughly as old as debian etch version. Did you add manually some repositories?

Can you do this:
apt-cache policy libc6
apt-cache policy libgtk1.2
apt-get -s install libgtk1.2 <--- this is a "installation simulation", nothing will be installed.

In any case, do not upgrade your libc6. You will probably end up in trouble.