IF I buy the 6 disc in-dash cd changer from a 01-04 X and replace the single disc player in my 2000, I was told about the different speakers in the 2000 and 01-04 models (4ohm and 2ohm) and how the swap will result in it being much quieter. First, can someone please explain the 4ohm/2ohm thing? and second, does anyone know a way to rectify thi without spending an incredible ammount of money? I'm a teenage boy, I enjoy loud music, but i don't want to spend a billion dollars upgrading my sound system It's fine like it is, I just want that 6 disc changer.

Yeah, I put an 02 changer in my 00. The 4-ohm/2-ohm speaker refers to the resistance they provide. The 02+ head units only have enough power to drive the lower-resistance 2-ohm speakers, and when hooked up to 4-ohm speakers they just won't push hard enough.
No fix, either replace the speakers, or get a line-level converter and an external amp. Or just get a non-OEM head unit in the first place.
Oh, and Nissan did have an external changer available for the 00 (SE only) that I see on Ebay now and then.

Brent

Thank you for your information, now how hard would it be to install a line level converter and how big of an external amp do I need?

Don't need much of an amp unless you want to fry the stock speakers. Not sure how much work it would be to install a line-level converter. Then again, I believe there are some amps that will accept the high-level output directly from the head unit, that's probably the way to go.