So I believe I have finally determined why this Compaq NC-6220 won't 'boot' Ubuntu ("loading grub... error 18") - and this is obviously because the BIOS is not able to 'translate' this 250 GB IDE properly for grub.
But as a 'rank amateur' with Ubuntu and Linux in general, I have to ask and maybe someone will 'enlighten me' as to why Windows XP SP3 will access and use the entire hard disk- and yet Ubuntu "Feisty" (9.04) cannot....? Sorta makes my bragging about Ubuntu kinda 'loose wind'... dammit.

I have no doubt this is most probably due to this very 'limited' BIOS in this laptop, which is really unfortunate.... HP does not have a 'newer' BIOS flash than what this is running (hmm... possibly there's a 'rollback' that might work? Hadn't looked at that...) - and there are not capabilities within the BIOS to reconfigure the hard disk for LBA or 'normal' or anything else, actually. It just "auto recognizes" the hard disk.
So I guess my great idea of sticking a really big hard disk in this little pokey machine is not gonna work, if I want this operator to 'experiment' with Linux.
Guess I'll have to go find a smaller hard disk and install on that.

Anyone wanna buy a brand new Seagate 2.5" 250 GB IDE...?? (jus' joking...!! big hard disks work for other uses, such as backups...)