I tried to install Linux on my sister's computer, and as it turns out, none of the bootloaders work with her system. As it is an old computer without specs (I don't know them) I think it may be hardware related. Is there a way I can get a smaller, or possibly an older bootloader to work a dual boot on her older system? And as I had to install a Linux bootloader to be able to dual-boot with Windows, I pretty much rendered their PC useless, and I feel terrible.

Symptoms:

Both GRUB and LILO have errors, from an error 17 in GRUB to repeating 99 99 99 etc for Lilo.

Tried:

Switching bootloaders
Switching where the bootloader is installed and changing which drive is primary in the BIOS....

Any suggestions?

if you want the "windows bootloader" back, so that only windows gets loaded, I've heard you simply need to do

fdisk /mbr

on the dos prompt. the way I got an older linux (redhat 6, lilo) work, was to install it not to the mbr, but to the Linux boot partition, after which I simply switched the windows partition non-bootable and the linux boot partition bootable (as far as I can remember; it's been some time). that worked. but I'm pretty sure it's not going to work in all systems, and probably you'll have to figure out your own ways I'd try a new grub or lilo instead of an older one, if they don't seem to work. also, there are other (3rd-party) bootloaders you can use to dual-boot, but I think they're not entirely free of charge.

Sounds like a geometry mismatch. Maybe the drive is CHS based, and if (as is almost certain) you installed the loader from a liveCD (or install disk) it would be configured for LBA.

Check the BIOS for disk mode - in need you I believe you can force the geometry in grub (I haven't done this). Will need to be done from the grub prompt, and then setup run.
Hit the website for doco.
As above, "fdisk /mbr" run from a boot disk should get Windows back. For Win2k and later, boot the CD, and run "fixmbr" from the recovery console.

Next time I'm in Seattle I'll have to try that. They bough a brand new 200 gig harddrive, so I'm sure if I activate the boot partition on that drive and write LILO or GRUB to it, and set the BIOS to load that drive first, It might work. I'm not sure if I already tried that, but now I have a path to follow, at least.

And if nothing works, I'll just run 'fixmbr' from the recovery console...

Thanks for the ideas. The more the merrier, and I'd still like to hear some suggestions. The thing is, my sister and her husband are pretty politically against Microsoft, so I thought it was worth a try to give them everything they need in a PC for free, rather than having to pay for it.

Thanks a lot, again.

I have another question: will fdisk /mbr erase the entire harddrive? I shouldn't think so, since /mbr is directing a reformat of the master boot record, but fdisk is scary, and they have a lot of files they need on the harddrive.

Yet another question: if I run fixmbr from the recovery console (because the OS in question is Windows XP) is there any chance of it formatting or erasing any data on the harddrive?

The reason I'm asking this is because they have work they really need to get done, and i haven't been up there since, and I feel horrible for leaving them with such a large OS for such a small computer.

The fdisk we are talking about is M$ofts - that "fdisk /mbr" is a DOS command. The fixmbr is for later O/S's - use one or the other, whichever is more convenient. The latter is documented, the former was kept in the closet - both do the same thing. Neither will trash any data, although you'll likely get a "this may destroy your world, and kill your cat" message. M$oft wrote the utilities, so they should know.