Change the on rollover to include the image

Hi! I would like to have the images in the sub-blog "squares" on the front page of the Network theme also respond to the on rollover to refer to the posts (now if you rollover them, nothing happens). (Ok, Ok, just like wordpress.com) I am a bit confused about which files are controlling the front page but if I can navigate my way around, I am comfortable making some simple edits.

Thanks in advance,
cmccb