JTAG Software Tools
Although the Openmoko Debug Board is thought for ARM processors, JTAG is not specific. The Openmoko Debug Board uses a FTDI chip to control a serial (RS232) interface and JTAG through USB. And, there are Linux drivers available.
OpenOCD is a free and open software to do the debugging.
So we think that we can use it...
We just have to find out how to use and configure it for MIPS processors (you need to write some machine code into the instruction registers to have the memory controller read/write the NAND flash).
Here is a link where some guy did use OpenOCD for MIPS:
(E)JTAG for MIPS: http://www.linux-mips.org/wiki/JTAG (this page says that OpenOCD just supports ARM processors?)
A low-cost EJTAG interface and daemon software: http://www.totalembedded.com/open_source/jtag/mips32_ejtag.php
Here, some guy did unbrick a Neo 1973 using OpenOCD: