Your navigation jumps about like a hamster on a hotplate! And your footer scrolls over your fixed left column. That's because the top and bottom parts of your middle section headed "welcome", don't line up. So you need some adjustment there.
There are a few ways to make a version of "position fixed" work in IE6 but they can compromise your ability to use absolute positioning elsewhere on the page and you will need to re-code. Likewise there are fixes for png transparency on IE6. Try googling and you should find both.