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: 
**Run it inside [DOSBox](http://www.dosbox.com/).** That should solve your problems.

Their emulation is quiet decent, they have solved problems with EMS/DOS4GW/whatever etc.

I think it should run any DOS application pretty much OK.
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.