My system has a Radeon graphics card - partial output from hwinfo is

Hardware Class: framebuffer
Model: "(C) 1988-2005, ATI Technologies Inc. RV620"
Vendor: "(C) 1988-2005, ATI Technologies Inc. "
Device: "RV620"
Revision: "01.00"
Memory Size: 16 MB

I tried to install Natty but got the empty screen described in here. I've just got the system back up under Maverick and am not anxious to go through that again. I'd like to be able to test the grub settings for Natty before committing to the upgrade. Unfortunately I can't boot the stand-alone Natty CD (64 bit) either - the cursor shows on the screen, I can type stuff, but nothing happens (good or bad).

Is there any way to intercept or control the CD boot so I can try to figure out video settings that may be messing me up?