I'm able to create ad-hoc networks using DD-WRT but password doesn't work. Is there a workaround?
That's a very loaded question. DD-WRT is very poorly supported by their own devs... and is NOT supported by any of the manufactures whose devices it's running on.
That being said... you'll very quickly find that a lot of the wireless functionality is dependent on developers who reverse-engineered 3rd party firmwares in order to produce a mostly-working wifi driver. Unfortunately, many of the features don't work correctly. AD-HOC + any flavor of security is one such feature. Occasionally, you'll get lucky with specific versions of Atheros hardware & drivers... and it can work... but there is no guarantee it will. Your best bet is to either A) don't do ad-hoc + security on dd-wrt... or B) buy hardware that is designed to do it. (with their firmware)
On a side note... you might have some luck in the IRC channel on freenode... but my experiences in there have been not-so-great.