My father runs an old version of MacOS, I believe Mountain Lion, with a full set of Adobe apps, Suitcase Fusion, and so on from back when they were all 'buy-once' products. Reading around, almost none of it is likely to run on the latest version of MacOS without serious issues.
The OS's age has become a problem for almost everything else - the latest browsers won't run so more and more websites are unusable, and most downloadable software simply won't install (we had to dual-boot it with the highest OS that the hardware supports just to allow him to do iPad sync).
I've read that it should be possible to buy a newer Mac and run a virtualised copy of Mountain Lion in something like Parallels. Presumably it would then be possible to transplant an image of his old boot drive to be able to run the creative software.
Is there any reason that doing so might not be a good option? And can anyone comment on how well old Adobe apps run inside a VM, both in terms of performance and potential compatibility issues?
(The creative software is the main thing he uses the Mac for, so if it's going to be sluggish or painful to use in practice then maybe a different plan would be better.)
Edit: Sorry - a bit more detail!:
iMac 24-inch, Early 2009, 2.66GHz Intel Core 2 Duo, 8Gb DDR3, Geforce 9400 256Mb, upgraded with an SSD boot drive
OS X 10.8.5, and Adobe Suite CS5
(No specific model in mind as an upgrade, min spec recommendation welcome)