Ubuntu 10.04 bad install...now Mac won't boot

I've been having a problem all day. It all started when I tried to partition my HD to install Ubuntu with bootcamp on my mac. The install froze and when I restarted the Apple logo was replaced with a "do not enter" sign (circle with slash). I've been searching forums for a solution and even tried to run a LiveCD but that failed. I think I need to remove GRUB from my MBR. Anyone have some suggestions/help? Much appreciated.