Just FYI, I've recently updated the OpenOCD Debian package in unstable. OpenOCD is a Free Software JTAG utility which currently supports quite a large number of JTAG adapters and various CPUs/targets (many ARM and now also some MIPS ones). It's being used by a number of Free Software related projects such as OpenMoko and many others.

Here's an example of how you usually use the (new) OpenOCD with a cheapo parallel port JTAG device. First, start the OpenOCD server, providing it an interface config file and a target config file (you can copy/adapt them from /usr/lib/openocd/{interface,target}/*.cfg, or use those files directly if they work for your target, of course).

$ openocd -f parport.cfg -f lpc2148.cfg

Then, in another xterm for example, connect to the now-running OpenOCD telnet server. Here you can now run various commands to probe, control and program the JTAG device(s). Try help for a list of commands. As an example, for flashing a binary onto some LPC2148 eval board you would do something like this:

$ telnet localhost 4444
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
Open On-Chip Debugger
> reset init
JTAG device found: 0x4f1f0f0f (Manufacturer: 0x787, Part: 0xf1f0, Version: 0x4)
srst pulls trst - can not reset into halted mode. Issuing halt after reset.
target state: halted
target halted in Thumb state due to debug-request, current mode: Supervisor
cpsr: 0x800000f3 pc: 0x7fffd2a2
requesting target halt and executing a soft reset
target state: halted
target halted in ARM state due to debug-request, current mode: Supervisor
cpsr: 0x800000d3 pc: 0x00000000
> flash write_image /home/foo/program.bin 0
wrote 1236 byte from file /home/foo/program.bin in 0.533683s (2.261701 kb/s)
> resume 0

The final resume 0 will start to execute your program on the ARM LPC2148 microcontroller.

Check out the openocd info page (info openocd on the command line) for lots more documentation.