If you can find a deb file by any chances, don't use rpm. rpm files are for RedHat/Fedora distributions and their relatives (SuSE, Mandriva, ...) Ubuntu is based on Debian, and uses Debian's package system (.deb files).
To install a deb file
Code:
sudo dpkg -i filename.deb
This tries to install the given deb file, if all the dependencies are met (other packages are also installed, which need to be installed for this package to function properly). If the dependencies are not met, the package is not installed, because it would not work anyway. This is the case with your rpm file also (but still use deb files, it's less messy that way). When dependencies are not met, you need to find those depending packages (packages, that have the files that are needed before the original package can be installed) and install them first. This can be a lot of work sometimes..
Better method is to use a package manager, if you have internet connection available. It works a bit the same way as dpkg, except that you don't give it a file name, but a package name which it then tries to find and download from specified "warehouses" in the internet (called reposities), along with all the dependencies which it will try to download too, and if it does find them all (it should), then installs them all for you. So even if that one package you want would need several other packages in order to be successfully installed, the package manager would do it all by one command (as long as the package is found from the reposities). Even if you're installing a single .deb file, you can try to install the
depending, missing package using your package manager, and after that install the single .deb file. To install packages using Ubuntu's package manager you can use the graphical Synaptic tool (or Add/Remove in latest Ubuntu versions) or from command line:
Code:
apt-get install packagename
Note that in the above command you don't type the package version number, nor .deb - just the package name.