No disk to install operating system

Sorry, I don't know where this should go so I put it in the basic forum.

So a couple of months ago i decided to change my desktop mac into a linux web server, and wiped the old snow leopard operating system off of it. Now I have decided that I don't need it that much anymore, so I am now trying to convert it back into a usable computer. I decided that as I couldn't find the Snow leopard install disk, I would download Windows 8, so on my laptop I downloaded the consumer preview, and then burnt it onto a disk, then put it into my desktop mac and tried to boot it up, however it said i had to partition it, but it seemed that I couldn't. So I searched for my snow leopard disk, and finally found it, when I inserted that, it asked me which disk I wanted to download it to, however, there was no disk that I could download it too.

I have a feeling I could have wiped it or something, but how do I get it back? I really want to use it again!!!! Please help, I know it was a stupid idea to change the operating system to linux. Is there anyway I can resolve the problem, if so can you reply, but remember I don't really have an operating system to check up on things on.

Thanks