Well that seems as if your Apps are crashing as soon as you run the phone. Are you Jailbroken or are you running stock? Have you tried updating to 2.0.1? I would recommend updating (if you're not JBen) and if you are try a restore and then re-Jailbreak.
My (non-jailbroken) 3G began acting like you're describing after I applied the 2.0.1 firmware update. Any app from the store would begin to run, then simply return to the home page. As an experiment, I downloaded one more free app from the store. Once it was done downloading and installing, my problem was solved for all apps. Give that a try.