As ehdwuld said (and to expand)
Open a terminal
type in "su" minus the quotes and hit enter
at the prompt, type in the root password (because, of course, no one runs as root regularly
)
type in "rpm -ivh compupic-5.1.1063-1.i386.rpm" minus the quotes and hit enter
when it is complete, type in "exit" and hit enter
type in "compupic" and hit enter (minus the quotes
If it fails to run, I would type in "whereis compupic" that should give you places it is installed, you could then try "path/to/directory/compupic" eg "/usr/local/compupic/compupic"
That should do it. If not, could you post any error messages you see?