Disk Utility can't repair; need to 'reformat' the disk- but can't create partitions because disk won't 'unmount'. Mac OS X 10.7.4 Lion

My MacBook Pro was running slow, I did the CPU% check and found two items were causing me problems: 'syslogd' was running up to 190 and 'mtmd' was running up to 94, both well above anything else I was running. I tried to quit them, but since they were both coming from the user 'root', that did nothing.

I didn't know what to do about that, but I did know it was useful to verify the disk, it found red errors once it had finished, so I ran Repair Disk, but it said 'Disk Utility can't repair the disk.' Its advice was: Back up files, reformat the disk, restore your backed up files.

I have Time Machine back up with an external hard drive, so I plugged that in. It hasn't been long since I backed it up, so I'm not worried about losing stuff I haven't backed up. I'm more worried that I'll make a mistake in the restoration process...

Where I am now: Following steps from the support site, I've tried to partition the disk, selecting the big 500.11 GB volume (on the far left, the intended volume Macintosh HD being greyed out), trying to put it into 1 partition with the GUID option, but it couldn't repair it because it couldn't 'unmount' the disk. I tried with two partitions, same issue. What do I do now?