Hi,
I was restructuring a quite large app with soft-reset/watchdog (avr/wdg.h) methods and accidently called these inside the setup() routine. Now my Arduino is coniously resetting and doesn't seem to accept attempts to upload new code.
Does anybody know how to get new code up to the Arduino or did I broke it? 
regards,
Eckard
The watchdog doesn't get stopped by a system reset, but it will by a power cycle.
You can try uploaded a fixed sketch using power-on instead of reset button to get into the bootloader, which MIGHT work depending on exactly which bootloader you have.
Related thread: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1234338562
Alternately, you can start looking at ways to reinstall the bootloader using the ISP header or external programmer.
Thanks for your posting, westfw!
My bootloader didn't let me upload new code (even directly after power-on).
Looking for an easy was to re-flash my arduino, I found a very good tutorial:
http://www.geocities.jp/arduino_diecimila/bootloader/index_en.html#top
It describes how to use the arduino diecimila-board itself as a simple programmer (with only a four-pin socked soldered to it and a few wires added)! If you have a windows-pc at hand, this is the easiest and cheapest way to burn a new boodloader!
So my arduino is up and happy, again. 
best regards,
Eckard