There are a couple different ways to do it- 1.) mod your ps2 hardware or 2.) use a cd/dvd thing that you insert before putting in your import game. I've done this a lot with the PS1 and GameCube, and I HIGHLY recommend the second option. It's a lot easier and less of a headache if you mess up.
Here's a PS2 cd import loader thing (first product in the list):
It's beginning to look a lot like Christmas. DSiWare (Monday) - Go! Go! Island Rescue! (500 pts) - Go Series Defense Wars (200 pts) - Flashlight (200 pts) - Spot the Difference (500 pts) Retail (Tuesday) - Art Academy - Bakugan Battle Brawlers: