PPP is totally separate from Adsense. It can be used as an additional monetization model along with Adsense and affiliate programs. Ads are basically random, not as targeted to the content so far as I've seen.
Code is basically javascript that you can include in your site and audio ads can automatically play when visitors view your site.
Do I recommend it?
At this time there's a lot of delays & flaws in the system that they have been working out for MONTHS! Not to say that it isn't a great concept and never going to work. But it's definitely not a revenue-generating program at this time. Stll in the testing phase.
With that being said it's your choice if you want to join now if you believe in the potential of this program. Just expect that you'll probably make very little money --if any at all (at least right now) until they get their stuff together.
I had the ads on a couple of my blogs and had over 700 PPP hits and only made a measly 4 cent. I've taken them down since and put them on hold since then - but am still monitoring the progress of the program.
Also Be Advised: Many of the audio ads ask your visitors to press a key on their keyboard to visit the advertised site. This can easily take your visitor away from your site. (Adsense diverts your traffic too but at least they pay a little more at least right now as I've seen). Some people are ok with that, some not. Just wanted you to be aware.
Hope this info helps