UNIX costs money, Unlike GNU/Linux, for the most part it is not freely offered and can be quite expensive. And may not be the best to learn on considering its cost. What if you pay a license fee of (
SCO was asking about $1,500 Per CPU License -thats another story) say the $1,500 and still cant get it to work?
I have installed Slackware Linux on an older Compaq Armada 7800 (300Mhz CPU) some time ago, just finished replacing the LCD CCFT and inverter this weekend. But for a laptop running X it does fairly well.
On the ISO's you burnt for Mandrake-Linux, there are floppy disk images included, usually you need to run the included 'rawrite' program to create the boot disks.
Instead of using GNU/Linux, you could give one of the free *BSD's a try. If you can't get an OS on the laptop, then you have not tried NetBSD. It may be harder to install if your new to the *nix platforms, than a GNU/Linux distro, but it runs on just about anything with a cpu.
The BIOS would have to load, your just not seeing its output. You must have a Compaq, which usually displays a splash screen. You might need, if it is a Compaq, a specific floppy disk to access your BIOS settings.
http://www.netbsd.org