When doing the font selection in the CSS file for this blog I came across a great little resource. It helps you decide which fonts to use in your design by not only providing the Mac equivalents to standard Windows fonts, but also showing you what they look like side-by-side. There are also a couple of screen captures showing the fonts in Windows 2000 with Internet Explorer 6 and another one in Mac OS X with Safari 1.2. Very handy!
Common fonts to all versions of Windows & Mac equivalents (Browser safe fonts)