and just to confuse things, XP can have IE7. My downstairs one has ie7 but it doesn't work properly. (now, why did I say that as if I was surprised?)
Um, am I the only one wondering how vertical space should change anything? If it does, you've designed badly.
I hope you noticed that most people don't browse full screen so you'll have far less real-estate than one could expect. My browser window's set less than 1024 by 768, for example, even though my monitor's native is 1280 by 1024.