If you're serious about web design and how your sites will look across different platforms, it would be a good idea to buy a copy of an application which can run PC programs on the Macintosh - such as VMware or Parallels. You can test the site in IE 6, IE7 and IE8, depending on which versions you load and according to the version of Windows you load on the partition used by the application.
If you have a multisync
monitor you can set up your screen with different resolutions which
will accurately reflect what happens when people view the site with
various screen sizes.
You can also see a static "screenshot" of your page by using the free service at NetRenderer. As this is static, you won't see any rollovers or galleries working, but you can see if your layout has any issues.