When you mine with P2POOL I can takes some time before having any results (depends of the coin and traffic).  When you get share it will give you more part when the pool find a block. You will get paid only if the pool find a block.  If it is not clear enough you can have a look on my site. I have developed a small interface that is showing the bloc on the current miners payout it is fun an really more easy to understand.  Just have a look at the FAQ at  http://litecoin.p2pool-mining.org/stats/200 for more info. You may want also to try it.