This approach works on all packages ending in tar.bz2.
First of all open a terminal, by going to the directory where the file is (with Konqueror). Then press F4, and you will get a console. Then type:
tar -xvjf kopete-0.10.1.tar.bz2
When this has finished successfully, go into the unpacked directory with cd <directory> and type:
finish successfully or else you can't install this package. When it's done type:
And when this also has finished without errors, type:
It will prompt for a password. Type in the root password as you set it when installing your OS. Then type:
When it's done, your package is installed. If you encounter any errors, come back here