Enter Alien. This nifty little utility will convert those pesky rpm's into deb packages so that you can install them easy-peasy on a Debianish system like Ubuntu.
If you don't have Alien already, make sure you have universe repositories set up, and then, from the command line
sudo apt-get install alien
Now you are ready for this
sudo alien -k name-of-rpm-file.rpm
Dun-du-dun!!! You are now ready to install your package
sudo dpkg -i name-of-deb-file.deb