Zoetrope

Booting RHEL 5 or Centos 5 for the first time in Parallels Desktop (build 3188) wil get you an instant kernel panic. Just include agp=off as a kernel parameter and the system boots and works like a charm (use 'a' at the Grub screen to edit the kernel parameters).

Afterwards you can edit the /etc/grub.conf to include agp=off by default:

 
title CentOS (2.6.18-8.el5)
        root (hd0,0)
        kernel /vmlinuz-2.6.18-8.el5 ro root=/dev/VolGroup00/LogVol00 rhgb quiet agp=off
        initrd /initrd-2.6.18-8.el5.img