Peter,
You may also want to take a look at the Vectric products, they are simple to use and run on Windows.
http://www.vectric.com/
You may find EMC2 difficult if you are not Unix or Linux savvy.
Mach3 is Windows XP based and very good.
Spend some time reading on the Mach3 forum, it will help a lot.
http://www.machsupport.com/forum/
You may not need to replace your steppers like the other forum members suggested, try them first.
The older round steppers do not develop the power that the new style square units produce.
If they still perform well you have saved some money.
I think that using the antiquated DOS based software will be frustrating and limiting, however it might still be a option.
Enjoy the challenge, its addictive.
Jeff...