still, a Blinking folder with question mark

I've read just about every forum on the net for the past 9 hours and i'm seeing the same answers, however, my situation just seems a lil different. I have a duo core imac g5 and after i use my windows cd to uninstall and reinstall my partition ive been recieving the "folder of death". currently there is no operating system on my mac and for some reason the only thing it recognizes when i hold down option is my winxp cd...please help me get past the grey screen so i can reinstall mac osx and leave pc behind..

Have you tried holding down "C" instead of option to boot from the cd?