On the fly unzipping

Hello, I was hopping that one of you would know how to setup a self-extracting php program. This is the story: I'd like to offer a zipped file for download. Someone unzips it on their PC and there find two files, "extractor.php" and some other file that php can unzip. They upload these two files to their server, direct their browser to extractor.php, enter some information, and extractor.php unzips the other file into multiple directories/files, each adjusted to the specifications set in extractor.php. I know there is a way for php to unzip files such as .elg, but how to do it, and if the server needs to be set up in some special format... I don't know. I've looked around on-line, but so far haven't found anything. Thanks for any input, Sean