problem with imac start-up

i just installed windows on my mac and then unistalled because i found it useless and now every time i start up my computer it asks me to put in a boot c.d unless i hold down option key. is there a way to change preferences so that it will automatically start up as mac HD

When you installed WINDOWS....you probally formatted it to all there... and when you deleted it.. you deleted everything....so kinda...your screwed...lol, unless you re install it again.

and format it so the mac has more memory and all. THEn... delete it lol