I use Slackware, because selecting each softwares manually to be installed or not is needed for constructing a minimum system comfortable for such a low-spec machines.
For building Japanese environment, see PJE (Project Japanese Environment) distribution add-ons.
Here I will wrote some 230Cs-specific notes for configuring Linux system.
Mouse support (not serial mice) [Y]
PS/2 mouse (aka "auxiliary device") support [Y]
Advanced Power Management BIOS support [Y]
Enable PM at boot time [Y]
Make CPU Idle calls when idle [Y]
Power off on shutdown [N]
Sound card support [N]
% loadkeys defkeymap tp230-ascii-d.map
in /etc/rc.d/rc.local or so.