I've got a 4 Gigabyte flash drive that I'd like to make bootable. For right now, I need it to boot DOS or DS linux. I'd like to have it boot to grub or something similar so I can select either one.

Your USB drive can be your emergency toolkit at home and away, and if the host machine supports booting from a USB drive, you can boot to a USB key that you've prepared in advance. USB drives can boot ...

Since MS-DOS doesn't support USB devices, I'd suspect that the BIOS would have to support the device natively as a bootable drive before you could achieve anything like this-- and even then it would ...