It seems you don't have a clue about your computer, do you? (I don't mean to be rude, just curious.)
To find out what Mac OS you have, go to the Menu Bar >

> About This Mac.
If it's version 10.4.x (x being the numbers from 0 to 11), then it's Tiger, if it's version 10.5.x (x being 0 to 7), then it's Leopard.
Also you can use Spotlight (CMD + Space Bar) to search for files, if you know the name.
The Core Duo is your processor/CPU (the computers brain, doing the calculations). It is from Intel, which means you can run Windows via Boot Camp (in Leopard, an expired beta in Tiger) or via a Virtual Machine like Parallels or VM Ware Fusion.
If you have Leopard (10.5.x), all downloads go into Users > you > Downloads, when you use Safari as a browser.
If you have Tiger (10.4.x), all downloads go into Users > you > Desktop.
Why did you buy a Mac in the first place, and why took it so long until you realized, that this computer (more specifically the Operating System) is not cut out for you or you not for it.
It's just like spinach, some people like or love it, others don't.
Or like a glass of water. Some like it half empty, others like it better half full.
Or whatever....
It's a preference, one doesn't have to like it, if it's doesn't suit one.