Yu-Gi-Oh! GX: The Beginning of Destiny Cheats

Card Passwords
Go to the Lab, when it finally appears, and choose the password machine. Put in the following codes- note these cards will appear in the rental shop and you will be charged a fee that will come out of the duel points you win (I have more, but, I was unable to put them all on the form that Gamefaqs has provided):

83994646: 4-Starred Ladybug of Doom
67048711: 7
23771716: 7 Colored Fish
14261867: 8-Claws Scorpion
49140998: A Feather of the Phoenix
21597117: A Hero Emerges
00295517: A Legendary Ocean
05728014: A Rival Appears
13026402: A-Team: Trap Disposal Unit
40133511: Bazoo the Soul-Eater
35215622: Blindly Loyal Goblin
26376390: Copycat
34124316: Cyber Jar

Unlock Midday Constellation (Noon Star) Booster
At the shop screen where you select the boosters, Enter The Following Code:

[Up], [Up], [Down], [Down], [Left], [Right], [Left], [Right], [X], [O]: Midday Constellation Booster

Free Stuff
Try doing this in order to get three free cards and 10,000 DP. Keep in mind that this can only be done once per save file.

Step 1 - Connect your PSP to the USB port on your PS2.
Step 2 - Insert Yu-Gi-Oh! GX Tag Force 2 into your PSP, load the game, select "Database" and then "USB Connect".
Step 3 - Insert Yu-Gi-Oh! The Beginning of Destiny into your PS2, load the game, select "Database" and then "USB Connect".

If done properly, your prizes should be won thereafter.