[CentOS] GPT?

>Can I do this from an install though? Or should I use a LiveCD? The
>drives in her ewont boot at this point.

The install DVD will let you boot to a "rescue" mode, instead of typing "linux".
Once in that mode, skip net and install scan. Then when you drop in to a shell,
go into parted. You are installing to sda IIRC? Try:

`parted -s /dev/sda -- mklabel msdos`

Me thinks, as your system is not functioning and I *assume* no data of value
on any of the discs, you sure can't make it worse:)