i think you are on ubuntu? (can't keep up with everyones systems sorry). If so the debian packages will probably work: http://packages.debian.org/cgi-bin/search_packages.pl?keywords=gambas&searchon=names&subword=1&version=all&release=all
No no no, and a hundred times no.
Even if you know *exactly* what you are doing, do not reference a Debian repository on an Ubuntu machine. The resultant errors will be subtle, unpredictable, and quite possibly unstable. Both systems refer to packages with an identical naming system, but there is no guarantee that the packages themselves would be identical, or even compatible.
Using a Debian *package* on an Ubuntu machine is borderline OK, but you shouldn't install anything from random packages anyway. If you want to do that, go run with an RPM distro (OK, that was a troll :-)
Ubuntu is a *stable* system, not least because of the *lack* of packages that they support. If you don't like the package selection, then the idea is that you now know what you're doing, and move on to Debian. Especially when dealing with a beginning user, the answer should be "if it's not in main or universe, you shouldn't have it". There won't be a good reason for it not being in main, but there is often a good reason for something not being in universe :-)
Now, Ubuntu *is* a standard Linux, and has all the development tools available. I'm just saying that you shouldn't use them, not that you can't.
-jim
