How to install RPMs and DEBs on your Arch install
1. Get either or both of the packages rpmextract and deb2targz.
pacman -S rpmextract pacman -S deb2targz
2. Download the appropriate rpm/deb for the software you want to install. Be sure to ask around the forums or IRC channels the dependencies of these packages. Check to see if the repos already have these dependencies.
pacman -Ss pkgname
3. Get any needed dependencies that are not in the repositories.
4. Extract the RPM or DEB with the command(s):
cd /path/to/rpm rpmextract.sh rpmfilename
cd /path/to/deb deb2targz debfilename