You're running LION, right? The latest version of OSX.
I'm guessing you hadn't used the Recovery Disk Assistant tool to make yourself a rescue/recovery disk.
Hopefully it's just a missing bootloader or something like that. Data Rescue 3 - For Mac
has a good reputation.
What you really want to do is drop this question into a Mac forum since it's nearly a 100% OS question.
In your position I'd create a disk image before doing any troubleshooting. Just in case any troubleshooting goes awry.