Hi,
On the 770, fire up the web browser and go to http://maemo.org/downloads/
At the top of the page are lots of categories. Select games and browse the games. Pick one that has a big green arrow on it, and also says for 2006. Click the arrow and say 'open' on the dialog box that comes up. it will download the file, open the application manager, warn you about software not downloaded from nokia (select ok) and install the game.
It will probably be placed in 'extras' on the menu (rather than games) when it has finished.