XP Mode is an optional add-on that would require you first upgrade to Win 7 Professional, THEN you have to basically download a customized version of VirtualPC and then after that, download and install a copy of Windows XP into that virtual machine.
If you have a legal copy of XP, you can probably just skip all that and download a copy of VirtualBox. Otherwise, if this is a DOS program, there's also the possibility of FreeDOS. It's free, as the name implies, and their aim is to be 100% compatible, warts and all, with MS-DOS. So because MS-DOS has the rather shortsighted solution of himem.sys to handle RAM over 1MB, so does FreeDOS to maintain program compatibility. You could potentially download the free VirtualBox VM, and then install FreeDOS into that, at which point if the program runs inside this VM you have zero cash outlay again, and a working setup that should last a bit more indefinitely.
Longer term however, you really should be pointing out the increasing lengths that are required to train people on this equipment, and get the beancounters to factor those things into their TCO calculations. It's not always a matter of whether or not the equipment still works and can do the job, pretty soon you're going to have to develop your own in-house training program for it, and that will likely cost a fair bit of money. You have to be looking at secondary expenses that go beyond just the purchase price of new equipment and the upkeep costs. That will probably at least push the replacement date up a little, which is good, because your training system is getting increasingly fragile and convoluted. Anything goes wrong, it's going to be that much harder to troubleshoot because of all the extra layers you have added. And just buying an old refurb unit doesn't really help much either, because most of those components are old and have started oxidizing. Plastics become brittle, capacitor gel compounds start breaking down, parts rust, solder joints go cold, cables go bad, drive motor bearings seize up, the list goes on. You just trade one set of potential problems for a different set of potential problems.