Dispite what Cabbie states, the best way to improve your PR is to get links from pages with a higher PR. Send out 20 requests to exchange links and you should pick up a couple. A portion of that PR will be transfer to you. And yes, buying a link on a page with a higher PR will work. There is nothing wrong with this or that violates Googles policies. But the real question is why are you worrying about PR when you should be worring about ranking. Website traffic doesn't increase or decrease as a result of PR, but is affected by SE ranking.