I have downloaded Litecoin-QT, waited it to sync with the network, and tested some mining with CGminer & P2Pool. Even that I mined few hours with about 1400kh/s yesterday, I don't still see anything on my wallet. And, I also tried to search for for the wallet.dat- file from my Linux, but there isn't such file anywhere in the system.

I thought that this wallet.dat is generated automatically when client is started, but isn't it so?? What should I do to generate a wallet, and get my Litecoins from P2Pool to it? I have checked many times that the username (=wallet address) in the CGminer's configuration file is correct.