Browsers are as follows:
FF 3, FF 2 on MAC, Linux and Windows 21" dia wide screen (1920x1200) and 15" CRT (1024x76
IE 6, 7, 8 on Windows XP and Vista with 21" dia wide screen (1920x1200)
Google Chrome on Windows Vista (guess what 21" dia)
Safari on MAC OS 10.4 (hell if I know what screen size that box is about 15")

Are you using EM's for your text sizes or are you using %'s and px's? If the later it would explain the problem and the difference .