If you have a bootable CD and you boot that CD it boots to the primary partition on the first bootable device, is this not correct?
Well, sorta, and not really.... ;-)
If you are booting from a CD, the first bootable device IS the CD drive. Typically, a bootable CD will emulate a bootable floppy diskette, so you will actually be booting into A: drive, except A: drive is no longer your floppy disk drive. Your usual C: drive can still be accessed through its usual drive letter by typing C: at the A: prompt then pressing enter to return a C: prompt.
Your floppy disk drive's logical letter will now be B: and your CD drive can be accessed through whatever drive letter is assigned by the command line or configuration files which load the CD-ROM driver.
A bootable CD may also emulate a hard disk, but this is rarely done so I won't go into it here.
If I could I would just change the boot drive to D in the BIOS but this is a compaq machine and the BIOS is somehow password protected so I need another way.
Search around for default BIOS passwords used by Compaq. The password is usually "Compaq" without the quotes.
There are other password work-arounds, search the keywords bios, password, compaq on Yahoo or Google.