documenting some of the jtag thingies we've been fiddling around with
 getting your arduino to run on 3.3v TTL
as most of the devices around are running all there logic on 3.3V, you'ld better not fry them plugging your arduino running on 5V logic levels...
the arduino documentation explains you the arduino functions at 5V, powered from USB, or by an external power supply (fed with 6V or more)
we found out:
- you feed 5V to the external plug
- cut the power lines of the USB
then, the voltage regulator will regulate to 3.3V -- which the arduino happily accepts, running all logic on 3.3V.
we tried this on arduino duemilamove (atmega328p) and arduino mega (atmega 1280)
disclaimer: a 3.3v powered atmega 328p should,according to specs, not be clocked faster then 10Mhz, arduino is 16Mhz clock... so it's overclocked; we didn't have stability issues though.
 run arduinull or serjtag
lekernel wrote some code together to run a basic jtag finder on arduino. it still has issues (it can't find the jtag header on a documented powerpc 405gp board), but is promising (got succes on linksys BEFwhatever boards)
zoobab pointed us to this library( during Arduino_JTAG_Finder_Workshop) , to use arduino as a JTAG cable -- (do an hg clone http://hg.assembla.com/avr_jtag to have a copy of avr_jtag) to transform an arduino into jtag cable.
it would be great getting it to work on urjtag - hacking around with it tonight
 good jtag cable
- olimex ARM-USB-OCD seems the best hardware we got around now (in combination with urjtag tool which natively supports it -- using libftdi)