I don't know the programs you mentioned, but you could try running the software in DOSBox
DOSBox is somewhat games-oriented, but since the goal of the project is to fully emulate an X86 machine with DOS it might be able to run the software your client is using.
Another option would be to use one of the more "professional" PC emulators such as VMWare or Virtual PC. Those will require more configuration work such as installing DOS and the appropriate drivers for the virtual PC the emulator is emulating.
A third option would be to boot the system into plain DOS via a boot disk since Windows 2000 and XP don't offer any real DOS mode at all anymore apart from the command line which is a kind of emulation as well.
If the system is using the FAT32 file system for its hard disk, you will need boot disk that contains FAT32 drivers. The easiest thing to do is use a Windows 98 or ME boot disk since those already include support for FAT32.
If the hard drive is formatted with NTFS, it will probably be quite hard (if not impossible) to use the hard disk with "real DOS".
If the machine is used for Windows applications as well, I would probably check out the emulation approach first because loading the emulator is faster and easier than booting the system from a floppy.