There's a utility called Alien that converts packages from one format to the other. This doesn't always mean that an rpm will work on your system, though. You will need to install some prerequisite software packages in order to install alien, however. These packages include gcc and make.
Run this command to install alien and other necessary packages:
sudo apt-get install alien dpkg-dev debhelper build-essential
To convert a package from rpm to debian format, use this command syntax. The sudo may not be necessary, but we'll include it just in case.
sudo alien packagename.rpm
To install the package, you'll use the dpkg utility, which is the internal package management tool behind debian and Ubuntu.
sudo dpkg -i packagename.deb
The package should now be installed, providing it's compatible with your system.