For the moment, I have only 1 HDD 500GB.
Dual Booting is a totally different thing. Some find it easy, others difficult. I dont know how to go about doing that, but i know you need to install Mac OS X first. But that seems to be your problem.
OK, now you have got the boot cd working, follow those instructions, then when you switch to the Snow Leopard DVD, boot using -v -x and see if that lets you boot into the install proccess
PS. PM me so we dont take over this thread