Viewing site on Mac vs Pc issues

I did a website:

Renoskateboarding.com

and the issue is that when it is viewed on a pc via enternet explorer it alligns correctly, same witin firefox on a pc; but when you look at the site via a mac, it is unaligned. The columns are vertically higher than they appear on a pc computer. I built the site with a mac and had to adjust it for what most users have, but would like it to be visible similar on all computers. Any advice?