As NN said, you don't gret viruses with a Mac (we're major Mac people, here) But as to your second "hate" our sites have been hacked and thwacked, too.
Bastards.
A much simpler and cheaper solution to getting a MAC would be to install free anti-virus, firewall and spyware software. I have all of them and have never been hacked, hijacked, had a DoS attack or any such thing.
With regard to the site hacking... makes it harder for the hackers if you
a) have managed hosting so someone else gets to do the security updates for you in a timely fashion
b)If possible write your own scripts so that people arn't using common exploits of commercial or freeware scripts (people write tools todo this automatically)
c) Use the htaccess file to password anything you don't want them hacking... an example would be the admin pages of a bulitin board or forum. You are very likely to be using some kind of commercial or publically available system for this, which means you willl get hammered every time an exploit is found in it.
When I had a forum up on my site, it got defaced several times where people were taking advantage of an exploit, and doing so automatically by googling for the version number of the bbs software. Quick addition of a htaccess file to the admin directory stopped the nastyness as even tho they could still create fake admin accounts they couldn't get into the server to steal the htaccess password.
Even better where possible store your files in a non web accessable part of the server directory tree. If its stuff you want to display on the web (e.g. page content) get a script to re-print it onto a page. and if its backups or a database or something then you definately don't want it web accessable.