RAID 1 install

[James]

OK,

So I'm using the alternate media to install
a Raid 1 ubuntu server for network monitoring
(eventually nagios or jffnms).

I first used systemRescueCD to set up identical
(GPT) partition tables on 2 identical 2T seagate
drives.

1. The mobo is 5 years old and does not support EFI,
so it it  ok/possible to use GPT and not MBR ?

2. If so, which is what I'm trying, I'm following
section 4.1.2 in the "Ubuntu.serverguide.pdf
copyright 2010 Canonical....

So at step 4.1.2-2 I get this error message:

/dev/sda contacts GPT signatures, indication that it has a GPT table.
However, it does not have a valid fake msdos partition table, as it should.
Perhaps it was corrupted -- possible by a program that does not understand
GPT partition tables. Or perhaps you deleted the GPT table, and are now using
and msdos partition table. Is this a GPT partition table?
<yes> <no>


During those instructions, I was able to change the / partition to
bootable as the guide suggest. I'm not sure why I could not toggle
the flag, as I followed those (antiquated) steps verbatim.....


Some discussion and guidance is appreciated, as obviously I should 
answer yes, but, something is "boned_up" on this effort, methinks.


James