My CBmod has great AI thanks to Rollo.
http://imagemodserver.mine.nu/other/...arrierBattles/
PS: don't let the name fool you. Carriers are important, but bombardment ships, PD ships, close assault gunboats and troop transports are all equally important.
And, if you were to play against the AI on low bonus, they would quickly overwhelm your navy and then storm all your planets with troops

...Even I play against them on *No* bonus...
--
As for getting set up with PBW, first you will need to get yourself a login.
Visit
http://seiv.pbw.cc and register. You will get emailed a random password to use.
NOTE: The login is case sensitive!
NOTE2: When you visit, the first page you see offers a choice of graphical or text version. The graphical side looks better and works great for day-to-day use. If you get any odd errors, try the text side; it is sure to work.
Once you are logged in, press the games button (either the shooting-ship icon(graphics side), or the button marked games (text side))
This will show you a list of all the games you are in, and their current status (ready, needs empire, needs turn, processing in progress, etc) When you have joined some games, you can click the game name to go to the game screen. And from there, you can download your turns, upload your files, and visit the game's private forums among other things.
Since you are not in any games, the screen will be blank.
Click the "open games" or "all games" buttons (fleet icons in graphics mode) to view a list of existing games.
If the game has not started, and is not full, or if the game needs a replacement player, you can click the name to jump to that game's game screen.
There, you can press join (lightning bolt on graphics) to sign up for it. Once the game's owner accepts you, you can start playing.
Note: In the case of a new game, you will need to upload an empire file for the game master to use before the game can start.