PAL import games would have to be for NTSC region countries. If your machine is a PAL PS2 (most European, Oz, Nz, etc..) then you can play PAL games.

You cannot play NTSC without some sort of enhancement to your machine.

Online stores that are selling PAL imports are targetting NTSC countries. On the other side, NTSC imports are targetting PAL countries/systems. To play a game from a different standard PAL->NTSC or NTSC->PAL you will need a modchip, gameshark or some other method.

PAL->PAL should work perfectly. NTSC->NTSC should also work fine.

If you are unsure contact the online store and ask them directly. Further I'd check on their return policy just in case.