I have been developing a new theme too, and experienced the same problem (www.vikingprincess.net).
I know programming, but not web development.
I was APPALLED at how full of bugs IE6 is! It is beyond anything I have ever come across in terms of commercial software.
Developing in CSS HTML WP wasn't really the problem - working with IE6 was!
There are some so called IE hacks which lets you solve width and resizing related IE problems (bugs!). Search forums etc.
The other thing you can do is to stick to the smallest common denominator - i.e. avoid anything that breaks IE and go for 'simplified' solutions. This is what I ended up doing. My site is not finished, but there are already many features that are coded in clumsy way, since IE can nbot handled the stylish way of doing it.
On your site incidentally, the banner is nicer in IE than in FF actually! The sizing is better, I think.
All the best
Johanna