From Atomicorp Wiki
Forcing mock builds
/usr/sbin/mock-helper yum --installroot /var/lib/mock/epel-4-i386/root install buildsys-build
chroot: cannot run command `/bin/su': No such file or directory
build-sys archive (groups) isnt set up
Missing Dependency: rpmdevtools is needed by package buildsys-macros
this doesnt exist on CentOS3, so I used the one from Fedora 6. Backported and stuck it in the [atomic] archive. Then set the C3 mock config to use [atomic].