No you don't have to open up your computer. When most computers startup they display a logo for example your Compaq probably displays the compaq logo, when this occurs they usually say something like press del to enter setup, once you press the del key the computer would enter the BIOS. Now as far as your computer goes the key required to enter setup (Setup is the BIOS) may be different, but most manufactures use something like F1, F10, or del. Take a look at your computers manual to find out which key to press to enter your BIOS. Now as far as changing the drive that the computer looks at to boot off of this could be under several names it depends on your BIOS. Again take a look at your computers manual. It's most likely an option named something like Boot Device Priority or boot order or something along those lines and it's probably in a menu labeled advanced. ThatÂ’s the best I can tell you at the moment, I don't have a Compaq Presario 5000 so I can't give you exact instructions as far as what the setting is called and where it would be found in your BIOS. As I said above take a look at your manual for detailed instructions.
-GrayWolf