Theres few programs that do this, some install spyware, other you have to pay for.. Here is how to do it for free, and without having to install anything.
Download the latest version of DMG2IMG from here:
Extract the downloaded zip file.
To make it easier for people that do not know how to use the command line, drop the download DMG file in to the directory that you just extracted.
Now, open the console (start->run_cmd)
if the path where you extracted the DMG2IMG download was c:\users\yourname\downloads\dmg2img
then in the console, type cd c:\users\yourname\downloads\dmg2img
now type dmg2img yourdmgname.dmg anynameforoutput.img
preess enter, and you are done. now extract the img using 7zip, and you have your psw.