(note: also remember to click Refresh)
To answer your other question, on an x86_64 system, 0launch will pick all 64-bit binaries (if available) or all 32-bit if not. See arch.get_host_architecture().
There's some discussion of this bug on the mailing list:
http://thread.gmane.org/gmane.comp.file-systems.zero-install.devel/2728.
I've updated it to the latest versions from Debian/stable, and added the rest of the dependencies, so try it now (Preferences -> Help test new versions).
