Somehow my admin password (normally root/admin) has been corrupted. After installing dd-wrt, I turned off 802.11x and clicked 'Apply Settings'. Since then, I can no longer log into the admin interface because my root/admin login pair won't work. Also, since this is a fresh install, ssh is NOT enabled. I've tried holding the reset button for 20 seconds, and that seemed to re-enable 802-11.x (so clearly it did some level or restoring default settings). However, I still cannot login.
Any ideas are appreciated...
This did the trick for me (found from
http://www.dd-wrt.com/wiki/index.php?title=Installation):
While holding down the reset button, plug in the power cord. Hold the reset button for 30 seconds.