Hi Danish, Lisa,
Thanks for your prompt support!
I have now tried installing with my antivirus disabled (MS Security Essentials) - the behaviour is the same.
For the install logs, I'm afraid I don't seem to have an "installjammer" directory in either "Program Files" or "Program Files (x86)". I'm definitely showing hidden files, and to be sure, I typed the path into the address bar - no "installjammer".
Any other suggestions?
Cheers
Dave