I am probably going to slammed for saying this, but if you are going to write Bernina about a free something, why not write Microsoft and ask for the same? The changes that have made V4 unusable for you have come from the Microsoft end, not Bernina.
Also, the upgrade to V5 is not just so that you can use your software with Vista (Vista came out AFTER V5 did) but for all the other updates that come along with V5 (Monogram program, multihooping, etc).
If you ever get through to Microsoft
Why not ask them if they can provide customers with the OPTION of purchasing XP? Perhaps you can still purchase a used computer with XP? Maybe a Geek Squad person can load XP on a used computer. Computer programs in general (not just Bernina) are constantly changing, which is exasperating and makes it almost impossible for someone like me to keep up.
I share your frustration but be aware that is not entirely Bernina for your problem. If you didn't have enough to think about, there is a new Version 6 coming out this year. I don't know anything about it but perhaps there will be specials to encourage updating.