The iTrip takes two included AAA batteries. It easily snaps onto your PSP and replicates the headphone and AC-power jacks on the bottom of the unit. Griffin says you can get a minimum of 8 hours of streaming from two AAAs. That isn't terrific, so it's probably a good idea to get a set of rechargeables, although they won't recharge in the iTrip, even if you have the PSP power adapter attached.
Once connected, the iTrip fits with your PSP snugly and simply ends up looking like an extension of the device. To stream wirelessly, you need to pick an open FM frequency; you can toggle through three presets for optimal reception and switch between LX (stereo) and DX (mono) to fine-tune the connection. It's important to note that you're more likely to get a "quieter" connection when you go with mono sound because it's less susceptible to static.
We tried the iTrip with several audio systems and got mostly positive results. We had the best luck connecting to FM radios with digital tuners, since their numeric displays made it easier to match frequency numbers (87.9, for example). That said, we dialed in a reasonable signal with the Tivoli Audio iPAL, which has an analog tuner.
If you can tap into a set of good speakers, such as the pair of NHT ST-4 towers we used in one test, you'll be hit with decent and fairly big sound. We watched Spider-Man 2 and played several games, and as one might expect, the sound was far superior to the output from the PSP's tiny built-in speakers. We suspect that some people will use the iTrip with smaller audio systems, such as the iPAL, a boombox, or a minisystem, but even those speakers should be better than the PSP's built-in speakers. Of course, because it uses an analog radio transmission, the iTrip isn't immune to static or hissing noises, and depending on your movements and where you're standing, you'll most likely experience some interference from time to time. But overall, if you're looking for an easy and relatively affordable way to stream audio to a home or car stereo, the Griffin iTrip is a good solution.