AFTER four years of planning, rehearsals began yesterday for the next blockbusting musical to roll into Melbourne, the local production of Broadway's Wicked.     Perth-born stars Lucy Durack and Amanda Harrison sounded every note ready as they belted out No One Mourns The Wicked and The Wizard and I with the chorus.     "Can you believe we are all here?" gushed John Frost, the Australian co-producer, to the 32-strong cast.     "This is the most anticipated musical in Australia, websites have been talking about it for three years!"     Frost said he fell in love with the musical on Broadway five years ago.  The Australian version is the eighth, and Frost hopes it will "sit in Melbourne for a few years".     Rehearsals for the $12 million show continue six days a week until it opens on July 12.