banner appears off in osx browsers but it is fine in windows browsers

Question

here's a live example http://bit.ly/9JgNmN

tested in IE7, firefox, safari, chrome

in windows 7 seems to be centered but in osX the banner is off!

any ideas?

p.s.here is the original of the example that i have modified:

css-tricks.com/examples/InfoGrid/

Thank you

Will