Method of Approach?

Hey all,
I’m about to embark on my first full flash site and I’m not sure about how I should approach this certain aspect of the movie…
In my main movie, the background will be a picture taken of my actual desktop.
This desktop will load external swf’s into it. Im going to make the pic of the desktop grayscale. But, when a user rolls over a certain item on the desktop,(i.e. pencil, eraser, desk lamp,etc,) it will turn to color. I want these items as my buttons. Im just not sure how to go about making the item a button, and getting it to turn to color on a rollover. Should it all be done in photoshop? Import the items seperate into flash?
_in need of direction
Thank u all