Leave the floppy drive connected, and it will be the perfect or "classic" PC setup, in the old days: the PC would boot from the floppy disk. Then, as with most BIOSes of that era, it will attempt to boot from CD. When the boot process is 0 out of 2 tries, then it will boot from the HDD.
This is where PLOP comes in, if you followed those links given by birdmun, above. It loads USB drivers so you can boot off the USB. Or say you did not have time to burn an ISO onto a USB stick; this is where a linux live CD can be used. I won't spoil the fun by telling you what happens. That laptop may be old, but it's not a relic.