Here is a quick and easy way to center those pesky images and text in your blogger blog. It is a simple piece of html code. In your post or widget box, click the Edit Html tab that is just to the left of the compose tab. There, find your conent you wish to center and add the center html code before and after the iage or text. Make sure the last 'center' has a '/' before it.
<center>text or image here</center>
Using the center html code will then center the desired image or text in blogger.