Its possivel make a instalation of some software in ubuntu using a rpm file.One way to do this is using Alien, Alien is a program that converts between the rpm, dpkg, stampede slp, and slackware tgz file formats.

To do that, first you must install Alien, so in your ubuntu shell type:

$sudo apt-get update
$sudo apt-get install alien 

Now you can use the Alien to converte the file:

$sudo alien -k ficheiro_rpm.rpm

Now you are able to install the package:

$sudo dpkg -i ficheiro_deb.deb