Compaq PCs in general usually require that you press the F10 key shortly after the post. That should allow you to enter the bios and set the boot order. You may have to press the F10 a few times to ensure it happens at the right moment.

If your system will boot off of a floppy, you can dsee the following link: http://www.knoppix.net/wiki/Download...should_I_do.3F
Look for the Smart Boot Manager and insatll it to a floppy. Follow the directions on the site. When used properly, it should allow you to select a boot device.