Monkey Island is based on the SCUMM engine. Nothing to do with Sierra!! Take a look at http://www.scummvm.org, it's all there.
Play around with http://www.adventuregamestudio.co.uk/ for a while before starting your own blitz adventure game. It can give you some pretty good ideas. You probably also want to check out http://www.mixnmojo.com/ forums. You can ask there about how adventure games like MI where contructed, the people there are probably very willing to help you.
Play around with http://www.adventuregamestudio.co.uk/ for a while before starting your own blitz adventure game. It can give you some pretty good ideas. You probably also want to check out http://www.mixnmojo.com/ forums. You can ask there about how adventure games like MI where contructed, the people there are probably very willing to help you.