yum local repos first?

[Stuart McGraw]

i have a fc5 machine with a very slow modem internet
connection, so I set up a local yum repository holding
most of the core rpms.  With the other network repo's
disabled, I can install from it fine.

But when the network repos are enabled, and an install
has core dependencies, yum gets them all from the 
network repo even though many are available locally.

Is there some way to specify a repo "preference" so 
that the local repos will be used to satisfy dependencies
before going to remote repos?