[CentOS] retrieving specific packages from a repo

Hello,
	I'm setting up an additional repo on a 5.3 machine. I only want
three packages out of it, and to exclude all others. I know there's a line
to add to the repo file, googling didn't give it to me, anyone know how to
get only a selected set of packages from a repo? This is probably a very
simple question.
Thanks.
Dave.