Most people could probably only guess if this will work untill they try it. I want to use Ubuntu 5.10 and set up my sources.list to be an exact copy of the one on Debian 3.1 Sarge, so that instead of going online, My software on Ubuntu loads from the 14 Debian CDs. I hope that it will be just as compatible as doing it the normal way because Ubuntu uses Debian packages anyways. Has it ever been reported that someone tried this?

1 problem could appear.

The packages in ubuntu are newer then debian, you can run into a dependency hell, because package X requires version 1.0 of package y, but you have version 1.5 of package y.

But you can always try it.

I am going to have to run Debian if I want software. Ubuntu is my favorite distro. I lost my internet. That is why. Is Debian going to update its software soon? Does the different releases of Debian Sarge mean newer software?

I think that Ubuntu is based on Debian and that it also uses apt as package manager, but it does not mean that it uses the same packages: there is this version problem that mr_demilord pointed out and also the files often have different names (like Debian's "package1.deb" is called "package1-ubuntu.deb" in ubuntu).

Debian Sarge is the latest stable release of Debian, and as that it will change very little in the future. You can always use testing or unstable packages, but they on the other hand may change very often and anyway you would be very lucky if they match what Ubuntu wants.

You can try to do things manually, tho; getting the .deb files and installing them manually, but in this case I would recommend you to stick with Debian and then install the few packages that Ubuntu has and Debien doesn't.