How to definitively remove grub from my hard drive?

[Conrad J. Sabatier]

I've been grappling for the last couple of days with a rather
perplexing problems.  I want to install FreeBSD on a drive that I've
been using for Ubuntu, but I can't seem to get grub to relinquish
control of the drive when booting!

I've tried all sorts of methods, including 'dd if=/dev/zero
of=/dev/sda ...' (all the way up to the end of the first gig of space at
the beginning of the drive), I've destroyed and recreated the partition
table, I've used the FreeBSD CD-ROM's sysinstall's shell-out and used
the boot0cfg tool to install a new master boot record, as well as
FreeBSD's fdisk -B (which does the same), yet every time I reboot,
there's grub again (erroring out, I might add with either error code
15 or 17, depending on what I've tried just before rebooting)!

At this point, I'm ready to tear my hair out.  Does anyone know where
exactly grub resides on the drive, and/or how it actually loads itself?
Why wouldn't zeroing out the entire first gigabyte of space at the
beginning of the drive overwrite it?

I'm completely baffled, and could really, *really* use some advice on
this issue, before I wind up a stark raving mad idiot.  :-)

Thank you so very much if you can help me out with this.  I'm totally
out of ideas at this point.

-- 
Conrad J. Sabatier
conrads at cox.net