to run older DOS programs by emulation - that is, by running a virtual DOS environment. To be honest, I have yet to hear of anyone having much success with it, but you can certainly try to run your older programmes in compatibility mode within WindowsXP. This enables you to select a mode (Windows 95 for instance) which you wish WindowsXP to emulate, and you can then try to run the program.
Be warned that if you have a NTFS hard drive you will not be able to see any of your data files whilst you're in compatibilty mode.
To read more about this, go to start and click on help. When the help screen opens type: compatibility mode into the search box and click the green arrow