This is really confusing. There is no 11.12. Perhaps you mean 11.10. That
is not the only source of confusion. Aptitude does not search other
distros, so a GUI isn't going to help it do what it isn't designed to do.

The only applications that would search outside sources that I know of are
Ailurus and Ubuntu Tweak, but neither is in the repositories.

If there is such an app then I would be interested in it as well. Perhaps
you could tell us what you are trying to install and we could help that way.

I think Ubuntu Tweak is in Ultimate Linux 3.2, which is based on Debian and
Mint, but may be using Zorin source in the future.

Yes, I meant 11.10. The package installer I was looking for (and found) is
synaptic. Thanks for your responses.

Yes. Synaptic is good. It is my preferred package installer. It is no
longer included by default because they are pushing the Software Centre,
but Synaptic provides more useful information and has better filters. You
can display by source, broken packages, etc and it will show dependencies.

What Synaptic will not do is search outside the repos. It uses your sources
list. That is what threw me. Glad you found what you needed. :)