If you are in the US, then Bill is the way to go. If you are overseas somewhere, then send your PS2 to charlie_ps2 or dust2dust for installation. If you want the best of the best mod, then go with the Messiah 2. PS2 online does NOT check for a mod chip like xbox has done, so no worries here.
If for some reason this does start happening, holding reset for sereral seconds will disable your Messiah 2.