Hi Danish,
Thanks for your time this evening. I can confirm that the problem was indeed that my user-profile was stored on an NTFS Junction point on my filesystem. Following your suggestion, I created a new user profile on the local (non-junctioned) area and ran the installer from there. I now have Code Composer up and running :-)
I see now that junctions are mentioned in the troubleshooting guide (http://processors.wiki.ti.com/index.php/Troubleshooting_CCSv5), but under the "Installer hangs during installation" title - it might be worth changing that to "Installer hangs or crashes during installation".
Have a good weekend!
Cheers
Dave