Hi Chris,
Your Artisteer skin has some Javascript that is trying to ensure the content in the middle pane is as tall as the browser window. It's doing this to push the footer to the bottom of the browser window when there's not a lot of content on the site. The problem is that this javascript is being applied to all .art-content divs. I found this on line 520 of the script.js file. I think you might be able to make some changes to your theme.skin file and the layout.master file to fix this while maintaining Artisteer's intended purpose for the script.
First, open the theme.skin file and find the <portal:OuterWrapperPanel... control. Remove art-content from the CssClass property.
Next, within the layout.master file, find the <portal:LayoutPanel... control with ID="divCenter". Enter <div class="art-content"> directly before the <asp:ContentPlaceHolder... control within this LayoutPanel. Next, enter </div> directly after the closing </asp:ContentPlaceHolder> within this same LayoutPanel.
This should take care of the problem for you. There are better ways to do what Artisteer is doing, without script, but that would take a lot more work and in the end it would be easier to start with our Framework skin and customize it to look like your Artisteer theme.
I hope this helps,
Joe