Overclockers Melbourne has posted a guide to Reviving Your Ball Mouse.
Basically what you will need is a mouse (duh), some isopropyl alcohol or something like that, that cleans and disappears (which is the head cleaning fluid in the picture, you can obtain it >from any place that has DIY stuff for electrical dudes, like Dick Smith or something), a cotton bud or two, and also something thin and metallic, like a butter knife, or a nail file (metal), or a pin (something to scrape the rollers in the mouse).Read more