I can't tell form the code you posted but it sounds like it may be a box model issue. In IE two adjacent margins will collapse into one margin where as FF will render both margins.
The book below is great I have it and recommend it, the page also explains margin collapsing.
http://www.andybudd.com/archives/2006/01/what_i_want_from_css3_part_3/
Also just an FYI, you should separate your styling from your layout, makes your code cleaner and easier to understand. You should also give your divs meaningful names such as head, logo, nav, content, etc. Your div id's tell me nothing at first glance what part of your layout they refer to, i could probably guess based on your styling but why make it a guessing game?