Mmm. Even though the Vibrant is a more powerful computer than the PSP (it should be, the PSP came out 6 years ago), unlike the PSP it is not a dedicated piece of hardware.
The PSP has worse graphics, but better controller response and lower overhead for operations. The vibrant has to run Android and monitor the state of the cell radio/gps/wifi poll the touchscreen and supply data to any running applications or widgets.
This commercial has it right - www . viddler.com/simple_on_site/944cdc1b
Gaming will be a far better experience on a PSP, and its battery will last a lot longer than a Vibrant's