Japan is in the NTSC region. USA is in the NTSC U/C regions. Games won't work between them without a modded system, or assistance from HDLoader. Both countries use the NTSC video format and compatible power systems, so the advantage is that you don't need any special adapters for a Japanese system.
Originally Posted by entmike
A Japanese system is my means of being able to play my online imports (I got the system for FFXI when it launched in Japan) and use Japanese HDD software, which doesn't seem to work with a mod.
The only system I've ever had a mod installed in was a model 5001 PlayStation, and I'm annoyed with compatability problems that still pop up, so I've decided to just import systems to ensure compatability.
My PlayStation2 HDD guide.
NTSC J SCPH 30000 with HDD and PSBBN 0.32
NTSC U/C SCPH 30001R Astral Blue LE PS2
Final Fantasy XI status:
Server - Ragnarok, Race - Mithra, Jobs - BLM 72 WHM 51 SCH 39 SMN 25, Nationality - Windurst, Name - Bungiefan