Congradulations , I absolutly love this site. i talk about it a lot. And i just found it by accident one day in class when i was really really bored. I think that was about 5yrs ago now. And i still have yet to post a picture.
i work in the paint department at a California based hardware store.
You want to get interior wall paint. that will work just fine. if you want to do detail craft paint will work but you will need to get a clear coat (acrylic not oil) to put over the design to protect it. before you do anything you want to clean it, if it is painted use TSP( they will know what you are talking about at the store) to degloss it. if you want to you can sand it down, but if you don't know what it is on it, you don't have too. If it is painted and you know how old the paint it, i wouldn't because there could be lead in the paint and you don't want to be breathing it. Then you will want to prime it for the best adhesion on your desk.
if you can, you should totally replace the draw pulls/knobs. To give it a kid feel. if you can't do that spray paint them a fun color and then put a few clear coats on them to protect the finish and help with the wear.
Also have fun with your colors. The mistint paint at your local hardware store is always a good place to find cool paints for an good price. Try for an enamel those are more durable.
just have fun. Splater paint might be fun, and your brother can help.