Question: Wordperfect 5.1 (for DOS) doesn't work without modification under Vista. How can I get it to work (as well as possible) under Windows Vista?

Answer: 
I would suggest creating a Virual Machine running DOS. You can download Virtual PC for free [here](http://www.microsoft.com/windows/downloads/virtualpc/default.mspx). You will need a copy of DOS to do the install.
Also info at <http://www.columbia.edu/~em36/wpdos/vista.html>