Zoneminder grinds my dual-core Atom to a halt. Try 'motion' for a simpler system (well, simple if you like config-file setup) with about 25% of the CPU usage. Plus, the viewing interface is just 'cd /motion; ls *avi' rather than the slow and clunky web interface of ZM.
It'd be interesting if someone could hack together something like motion, but takes advantage of hardware h.264 encoding. Even if just for still frames.