Limit the size of image?

This is a great looking theme, i really love it!

I have only one problem – sometimes i have odd sized images in the posts, and it seems that the plugin resizes the image somehow, but still i experience that some of the “posts” or “boxes” or what ever they’re called, are getting quite long?
Here is a screenshot to illustrate the problem: https://selectedbloggers.cphadsdemo.dk/scrndump.png

Hope you can help me, thank you in advance

/jaze