For new players and experts alike, playing a quick game on the computer every once in awhile is always a good idea, so take a look at PokerTH, an open-source game that brings the best of Texas Holdem right to your desktop.
PokerTH allows you to play online through its servers with people from all over the world, or you can play simulated matches against the game's AI. You also have the option of creating network games, although you'll need more than one computer connected to the local network to be able to play with other people.
The rules are the same as in real-life Poker: 2 cards per player, 5 face up, dealer, small blind, big blind... although unfortunately for all you card sharks out there, it's not possible to play with real money. Still, this is an excellent option to have fun and practice a little. It comes with various configuration options to adjust the minimum bet, starting money, and number of players seated at the table.