Navigation disappears in IE

I can’t figure out why I’m having the following problems in IE (that I don’t have in Firefox):

-navigation bar doesn’t show
-background doesn’t stretch to full screen
-clicking on posts opens in a new window (should be in a new tab)
-image and post column is extremely narrow and right aligned
-on sidebar–small green japanese ad shows to the right of the naminori 760 add. it should be below it.

This is my first wordpress site. My main viewers are Japanese and IE is heavily used there. Help for any of the above is greatly appreciated!!! Thank you!!!