Under Fedora and Centos:

[root@infra ~]# yum install yum-downloadonly

Be sure /etc/yum.conf contains : plugins=1

[root@infra ~]# yum reinstall gcc –downloadonly –downloaddir=/root
Loaded plugins: downloadonly
Setting up Reinstall Process
Resolving Dependencies
–> Running transaction check
—> Package gcc.i386 0:4.1.2-33 set to be updated
—> Package gcc.i386 0:4.1.2-33 set to be erased
–> Finished Dependency Resolution

Dependencies Resolved

Installing:
gcc i386 4.1.2-33 fedora 5.2 M
Removing:
gcc i386 4.1.2-33 installed 9.6 M

Transaction Summary

Install 1 Package(s)
Update 0 Package(s)
Remove 1 Package(s)

Total download size: 5.2 M
Is this ok [y/N]: y
Downloading Packages:
gcc-4.1.2-33.i386.rpm | 5.2 MB 00:00

exiting because –downloadonly specified

Now /root should contain : gcc-4.1.2-33.i386.rpm