Don't change the CDVD plugin from the default at this point, you're probably just doing something wrong.
(If it's saying it's not a PS2 disc, re-rip your game disc with ImgBurn.)
BTW - What game is this? (EDIT: Ok, I see the "god of war.iso".)
- Mark the Iso option under the CDVD menu.
- Browse for your Iso file with the Iso Selector under the CDVD menu.
- Choose to Boot CDVD (fast) under the System menu.
(If it's saying it's not a PS2 disc, re-rip your game disc with ImgBurn.)
BTW - What game is this? (EDIT: Ok, I see the "god of war.iso".)