you need to fully disassemble the phone to get to the trackball assembly. Use the HTC manual that can be found by searching it, it is a step by step process with all the screws pictured so you can get it back together. It is a tricky procedure, make sure you are up for a challenge if you have never had a phone like this apart before. this is one of the harder phones to work on.
BTW, Blackberry trackballs come out the front, by removing the trim ring. No such easy process on the G1!
"Son, no one gives a #### about all the things your cell phone does. You didn't invent it, you just bought it. Anybody can do that." -Dad
-G1 Early adopter
-Nexus with 3G issues
-Droid Incredible. Finally, a phone that works.
-Thunderbolt. Now waiting for the 4G to work correctly