OK - good question! rpms stands for "RedHat Package Management System"
which is really cool. There is also SRPMS which is "Source RPMS" which
will have the source code for a package. Usually this will be abreviated
as .src.rpm. The binaries you want to install should end in .ppc.rpm
as that stands for the architecture - so the intel world has .i386.rpm
and there is sparc.rpm and so on.

You can install a .rpm file in most cases by doing:
rpm -h -i package.ppc.rpm

There is help for rpm buy doing
rpm --help
or always
man rpm

If you have installed the source for some program like:
rpm -h -i package.src.rpm
Then, the source will be in the /usr/src/redhat directory. There
should be a file that will build and install the programs in
/usr/src/redhat/SPECS

To build a package from the source go into the /usr/src/redhat/SPECS
directory and run
rpm -bb package.SPEC
That should build the program and make the .ppc.rpm package in 
/usr/src/redhat/RPMS/ppc

I don't have the right rpm executable?
get the actual binaries at ftp://ftp.linuxppc.org/pub/packages/rpm/