IE7 vs. FF2 display in Panels

Hi, just downloaded and installed, great module and easy to use! One question -- I'm using the Panels module to display blocks in certain areas on the front page. However, when viewed in IE7, each container of tabs ends up being displayed under the previous one, whereas in FF2 containers are displayed side by side.

For example, I have a 2-column layout using Panels, and I have 1 container-block (a tabbed_block) in each panel.

So in FF2, it looks like this (which is expected):

CONTAINER1........CONTAINER2

But in IE7 it looks like this:

CONTAINER1
CONTAINER2

...even though there is enough room to display CONTAINER2 right next to CONTAINER1. If I go full screen with IE7, only then will it display as it does in FF2.

I think there's some sort of conflict with my theme's CSS (using a modified version of bluemarine), maybe with padding or margins?, but I'm not sure where to look. Any idea what might cause the containers in IE7 to display 1 per line, even though there is enough room to do so?

Thanks!