How to make yum seek alternative repository?

[Matt England]

How can I make yum seek an alternative repository?  I've been looking at 
it's man page and have yet to find anything.

Background:

My software development project wants to release .rpm packages via its own 
yum repository (we don't yet know exactly how to set up a yum repo, but 
we're assumign this is documented somewhere...and that we can make a repo 
with *only* our project's .rpms and not have to server others...if not let 
us know?).

However, I don't know how to tell our users to point their yum command to 
our repos while still inheriting the capability of the "standard" 
redhat/fedora yum repos for the package dependencies that we will have (eg, 
libc, Boost libraries, etc).

Any suggestions?  I'm hoping our users don't have to edit system config 
files to do this.  For starters, this is rather inconvenient and 
cumbersome; also, this breaks the ability to support non-root installations 
of software.

Thanks for any help,
-Matt