The only way to tell if a PS2 has a modchip or not is too take it apart and look at the motherboard.
If it is softmodded, then that has to do with the memory card.
To be able to load game saves from a USB drive, you will need a Cheat disk, or buy Swap Magic, or have someone install fmcb 1.8 for you onto a memory card.
What version PS2 do you have? Do you own any cheat discs?
Try putting in a DVDR copy of a game with the memory card removed. If it loads...your system is has a modchip. If it does not load, then put the memory card back in, turn of the system, and re-try the test. If it still does not load, then the system is not modded at all. If it only loads with the memory card, then it is softmoded.
Model 90004 was when they changed the firmware to prevent softmodding...some of the earlier ones support free mcboot, the later ones do not. If you are lucky enough to have an eariler one, then you can use free mcboot to load ulaunchELF. This is a file manager that will allow you to copy save games (and whatever else) to and from flash drives and the memory cards. If you have the later version, then the only options you have right now are a boot disk (like swap magic) or a modchip.
