'Paralells for Mac' or 'VMWare Fusion' are the easiest. The cost is around $60 for these. They run on Mac OS X 10.4 and let you install DOS or any OS that runs on a PC (you must provide DOS or other PC operating system). There are free OSes like FreeDOS that may run your programs.
Bootcamp would work only if your programs will run under Windows XP or Windows Vista. Bootcamp is a free solution for Mac OS X 10.5 but you have to provide your own copy of Windows XP or Vista (not free).