You can still use old software, but you won’t get any support, bug fixes or new features. And when you upgrade your hardware, if it doesn’t work then you can’t use it - eg 64 bit Linux.
Shake was offered with unlimited licenses and source code for the price of 10 licenses which several companies snapped up. I have heard that Double Negative have put a lot of work into getting Shake on 64 bit Linux, but this is only possible because they have the source. It would be nice if more unsupported software had the source code available.
Simon


The new PC will require new OS, because the old one (if it is really old) will be unable to run or to run properly - no drivers, some kind of noncompatibilty. This new OS will not accept old software as you can not run a bunch of software in Vista. So this is the magic formula for kicking users to spend a lot of money for upgrading.