this mostly works like it should. I tested it on an fc3 system and a
rawhide system with some success.
let me know what does not work on your systems.
The config file stuff could use some love, of course.
you need to make one change to the default config file:
config['defaultroot'] = 'fedora-3-i386'
config['defaultroot'] = 'fedora-development-i386-core'
mach rebuild /my/favorite/srpm
and read the output.
see if it works for you.