Web-Based (Flash, PHP, etc) Software Installation

I need a way to make something like a web based Install package to install about a gig of files to the users computer, so it works like this:
user clicks link to go to a webpage, which has the installer code in it. he reads the welcome, clicks next, license agree, next, login using credentials found in readable form and SHA1 on a MySQL server, selects target destination on harddrive, and lets the page stay open overnight while the script loads the files onto the computer. then in the morning, after download, the user is able to use the files.

sort of like the flash installation that Adobe has on their website.
~tks~