While playing around with themes from StudioPress I learned about TimThumb. I managed to get it working with iBlogPro3 from PageLines. IMHO much easier than doing it the way the theme author suggested. If you’re curious the changes need to be made within library/_posts.php find the line that deals with the thumb images and change it too something like the following. I choose to also create a tools directory in the root folder and put timthumb.php in it. Also make tools/cahe and make sure the webserver can write to the directory.
<img src=”/tools/timthumb.php?src=<?php echo $postimageurl?>
&h=200&w=200&zc=1″ alt=”Post Pic” width=”200″ height=”200″ />
When all is done and working, you can simply put the img url in the custom field and timthumb will automatically size it accordingly.