Or a new EPROM burner. 😉
Generally, most desktop machines still allow installing DOS, or at least copying a working installation from another machine. Unless they use EFI instead of BIOS, or the graphics card is not VGA compatible, it should work.
I've had good success with the DOS that's built into Windows 98SE (aka MS-DOS 7.1). Just make a 2GB FAT16 partition at the start of the hard disk with some CD-bootable partition management program, boot DOS from a floppy or boot a Windows 98 "rescue disk" floppy (an external USB floppy drive should work with the right BIOS settings, if the MB has no connector for a real PC floppy drive), FORMAT C: and off you go. As for parallel ports, if your modern MB doesn't have one you can get them on PCI cards and usually there exists a DOS program to configure them.
My Core2Quad system happily boots into DOS 7.1 and except for the sound card and non-standard USB devices I can use most hardware without problems from DOS.