as much as I hate IE, I need to design my sites for IE as most mugs still haven't switched to a decent browser yet....this means that whoever designed the theme you're using probably did so for IE, and how you see it is likely how it's supposed to be.
I use IE& and most likely always will use IE7. I hate firefox and its varients, Opera just looks plain ugly and mozilla is like firefox, to much hassel to be worth it.
IE is simple, i dont have to faf around to do stuff with it. So long as you have a decent firewall and virus checker there's no problems. I've been using IE for years and ive only once encountered a problem that was related to IE itself, the rest have usually been my error, or 3rd party software error. I'll never understand why people keep knocking IE.
As for the theme, it eorks for me, ive tested resolutions from 800x600 and up. Problems start when you go below the 800x600 res, then it looks all squished. However i think its safe to say most people dont have a monitor below 800x600