Sure thing, apologies if any of this is too dumbed down.

I uninstalled pygtkeditor and python-pygtksourceview completely first.

You'll need to do the below as root so be careful.
Please make a backup of the below files first - just in case.

Then I had to edit:
/var/lib/apt/lists/repository.maemo.org_extras_dists_chinook_free_bin ary-armel_Packages
and
/var/lib/dpkg/status

(You can get the info for these by typing 'apt-cache showpkg python-pygtksourceview' as root in your terminal)

Search for the entry for python-pygtksourceview.
It's "Depends:" line lists libxml2juuiiii, change this to libxml2 in both of the files.

After you've done this, don't update the application list or it'll overwrite your changes.

Then install pygtkeditor. After it's installed, don't upgrade the python-pygtksourceview package or you'll be back to square one.