sorry if these are basic questions but if I buy a domain name what is it you do for it not to show the usual iweb address for the site?
Basically, the easiest thing to do - although many might recommend that you register with one ISP and host with another - is to pick an ISP, get a plan, and register a domain name with them (each ISP has a slightly different page for registering, but they're pretty similar).
So, suppose you want "www.mysite.com". [Edit: apparently, this is a real domain... I'm only using it as an example, though!]
You'd pick an ISP and get a plan... whichever one you decide on.
Then, you'd use the ISP's site to register "mysite.com". You might need to try a few variations because so many domain names are already taken.
Then, once you've registered, if your ISP is like a lot of them, you'd log onto your account (Telnet, FTP, using Transmit, whatever) with your login and password, and there'd probably be a "mysite.com" or "www.mysite.com" folder (directory) in your account. You'd copy all your site files there.
If you're not using .Mac, there's no .Mac reference anywhere. If you use iWeb, by default (easily deleted), there's a "Made on a Mac" logo. No biggie. You don't need to leave it there.
When you make your files and upload them to your site, people just go to
www.mysite.com to see them.
and for the ISP's are mac's(iweb) supported by them all or does it not matter which OS you are using?
It doesn't matter. Pretty much all of them use browser-based access and allow you on also via Terminal.