Quick reply...
1. Don't ignore dependance. It was created by wise people to describe to users what should they do to have programs working.
2. Workaround for message:
Package must have "Section: user/FOO" to be considered compatible.

Run
dpkg -i /path/file.deb
command as root in X Terminal.

3. I understand you cannot use App Manager or apt-get because "internet bit of problem currently on n900". So, download a deb with PC, try to install in App Manager (find the file.deb in File Manager and open it, it will be opened with App Manager);
if it refuses to install, read log;
if there are missing dependencies, install them first.
When you see 'Package must have "Section: user/FOO" to be considered compatible', just install through X Terminal.

4. To become root, first install rootsh package (downloaded by PC) through App Manager, and then type
sudo gainroot
in X Terminal.
But be careful! When you are root, type only the commands you understand clearly. Don't just type random letters and commands.