The development version of leJOS in SVN supports I2C writes and has an RCXLink class that supports the mindsensors NRLink adapter. It supports several different ways to communicate with the RCX, including remote motors, remote commands, support for RCX opcodes via the Serial class, and support for Java streams with RCXPort. All this will be in the next release.
There is a snapshot directory in SVN.. If you get snapshot/bin/lejos_nxt_rom.bin and snapshot/lib/classes.jar, it supports the code in the latest i2c.c.
If you want to build a cross-compiler, the instructions are at http://www.jstuber.net/lego/nxt-program ... chain.html