A usb is kind of a pain. Go here
to get free software and instructions to make a usb pen drive bootable, method 2 might be the easiest. then follow the instructions from the readme.
The readme mentions a bios iso file you can burn to a cd. this might be way easier than the usb method. if you don't have iso burning software download imgburn, it is free and super easy. Just follow the instructions from the readme.
If those don't work a USB floppy drive will. but we'll wait to see if one of the first 2 methods work first.