Reporting back following my purchase of an iMac - thanks to all for the contributions which helped my make the decision.

I chose to purchase Parallels - the public-domain offerings don't seem to be available for Mac OS X Mountain Lion - and have found it very user friendly.

One of Parallels's excellent features is the ability to "migrate" a complete Windows setup to the Mac, which simply clones the PC to a virtual machine on the Mac. It does insist on your entering the Windows registration code, which I found stuck to the bottom of my laptop.

This way I was up and running very quickly on my Mac, without even having to reinstall BIAB!

So far, I haven't discovered any flaws in the running of BIAB, and am able to spend time on migrating my other files and applications to the new environment.

One other agreeable feature of Parallels is that it also supports a pre-packaged version of Ubuntu 12.04, so I can simultaneously browse my collection of photographs using "Shotwell" in a Ubuntu window, while listening to BIAB-generated music in an XP window and keeping track of my mail on the Mac itself.

I also have a Windows XP Professional Virtual Machine set up - this allowed me to migrate a legacy accounting package, for which I no longer have the distribution discs, and for which I occasionally had to boot up my desktop in Windows instead of Ubuntu.

No doubt I'll find something to complain about once the honeymoon period is over...