if im not mistaken.. the DS1820 is a 1wire device. There is a command that you can send, that will get the 64bit address code from each 1wire device you have. Since you know how to work one device, all you have to do is address each device individually with its correct address, and then get the information from it...
With one device, you can bypass the whole addressing since there would be no collisions occuring between multiple 1wire devices...
have a look at the data sheet...
or...if someone has the datasheet with them right now, they might post something a bit more useful