i'm not sure, so please confirm:
you have deleted everything by installing a bad installation of windows over your mac os volume?
if so, find the mac os re-install disks that came with your mac, put it in your mac and start it up holding 'c' see what happens, and then from the menu at the top, select start-up disk.
can you find your Mac OS X 10.4.6 volume to start up by?
Dual 1.8GHz G5 2GB, 1TB, Radeon 9600XT 128MB, 10.5
20" Apple Cinema Display + Dell 2005FPW 20" dual-head
iBook G3 700MHz 640MB, 40GB, Rage128 16MB, 10.4, dying battery