Problems with OS X update and 'enable journaling'
OK, so this problem had me tearing my hair out and cursing the big one upstairs for picking on me, but the solution I found to work is shown below:

Firstly, and this might not be necessary, but I used my Apple Application Installation DVD and held down the D key on boot, which tests the hardware to see if there are any errors. I tried both the quick test and the long test, together taking around an hour. 

Secondly I reset the PRAM. I'm fairly sure this did nothing to help my cause, but I put it here for a more complete answer. Hold down Command / Control / P and R, all at the same time as the computer is booting. It will reboot, at which point you can pull your fingers out of that weird position. 

Next, and I believe this to be the most important step, load Single-User mode on boot (Command + S). Once the command prompt is ready you should see somewhere in the verbose type above it a drive (something like /dev/disk0s2). What I did now was to use 

/sbin/fsck_hfs -f -d /dev/disk0s2

This debugged and fixed the drive in question, and upon using the 'reboot' command in single-user mode, the computer started up fine, and has been as good as gold since!

Regardless, this has taught me to back up my drives and also reinstall my OS on a new HD. 

Hope this helps anyone in the same leaky boat!
Ste