[CentOS] GPT?

Hi All,

I had a few 320gb sata drives that had OS X on them. Before that they  
were Windows for testing. I put them in an IBM eServer 335 and now  
trying to install CentOS 5.3

I get to the partition -> Create custom.

I take sda and create a swap and a software raid partition. Same with  
sdb

I then click Raid, mount at / and Raid1 (Mirroring)

I try to proceed and I get: boot partition is on a disk using GPT  
partitioning scheme but this machine cannot boot using GPT.

I have never seen this before.

Advice?

-Jason