Hello there

I am a brand new user, but I am enjoying discovering the joys of Drupal so far :-D .
I have installed Drupal-7.0-beta2 and I have slowly adjusted the appearance of my site page so far in a bid to try and make it unique :-/ .
I am however only just entering into the world of CMS es , from a world where anything was possible and easily acheivable from within one web development software package (namely Expression Web) .
The question that I have is:  How do I make my website logo into a transitional banner by adding script into the img tag.  I don't seem to be able to access the head section of my page and make any changes like I can with the main content bit.  I only managed to replace the logo with my own by replacing the default drupal icon that came with drupal 7.0-beta2 in the folders.
Apologies if this sounds naive and if I have missed a trick, but it is not obvious to me how to acheive that.
Just a little bit of guidance would be appreciated.

Basically I want my site logo (image file) to be swapped when it is hovered over, and then changed back to the original on mouseout.

Kind Regards
jayabee3