Using yum to install all sources

["Reuben D. Budiardja" <techlist pathfinder phys utk edu>]

Hello,
Is there easy way to install the sources for all the packages that I have on 
my system? Anyway to use yum for this, or should I donwload the SRPMS iso ? 
If I download the SRPMS iso, how do I install the sources ? Should I just 
"rpm -ivh *.src.rpm"  or something like that ?

One more questions, what's the different between the -devel package 
and .src.rpm (ie. srpms) package ?

Thank you for any help
RDB