Dosbox gets my vote. Great stuff.
If you don't know how to configure DOS, then I suggest you take a look at dosbox without even considering autoexec.bat and config.sys tuning. :-)
(Says the man running dual boot DOS7.1 / WinXP on his laptop.. I tuned the himem load areas manually since memmaker or qemm couldn't handle the Latitude C640 without crashing. :-D)