Slow respond and lag while playing game iPhone 3G

Slow respond and lag while playing game, some time will also auto drop out to main menu page, the worse case will hang up. Compare to iPhone 2G and iPhone 3G(using the same version SW and playing the same game), my iPhone 3G will only having these problem, it is surprising why iPhone 2G speed is more faster and smoothly than iPhone 3G? Did apple can release new update version SW to solve this issue, or apple can adding selection in Setting application to allow user to turn off all un-applicable application to speed up iPhone 3G? Thanks and looking for respond!
Compaq Presario Windows XP Pro