Instructions
Insert your copy of "Pokemon Pearl" into your Action Replay DS. Insert the Action Replay DS into the game slot on your Nintendo DS.
Turn your DS on, and select the DS Action Replay device icon in your DS's main-menu.
Select the "Code Select" option in the Action Replay's main-menu. Select the "Add New Code" option in the next menu.
Enter the name of the code in the text box of the name entry screen. You can enter any name you wish, but a name that identifies the code, such as "Obtain Turtwig," is preferable.
Enter the following in the text menu of the code entry screen:
94000130 FCFF0000
B21C4D28 00000000
B0000004 00000000
10001170 00000183
D2000000 00000000
Select the "OK" option to return to the code select screen. Select the "Obtain Turtwig" code, then press the "Start" button to begin playing.
Press "L" and "R" at the same time, then travel to Oreburgh City. Talk to the fossil guy in the city, and he will give you a Turtwig.