Tips for making an installer?

[eluser]MCrittenden[/eluser]
I'm working on a downloadable (and obviously self-hosted) web app and I need to make an installer for it.

The whole idea is that the user will visit an installation form which will allow him/her to enter database information, site name, etc. That information will be validated, put into config files (for example, database.php will automatically be filled out after the form is submitted), and a database structure will be built.

Any tips for doing this? Any projects that have already accomplished something similar that I could look at? Should the installer be a part of CodeIgniter, or should it be its own 'install' directory that goes alongside CI?

Any tips are appreciated. Thanks!