Banner Ads

[njdevils]

I am looking to start a free web hosting service (I know, original, arn't I?) and I am interested in using forced banner ads, like Tripod, Geocities, and other popular free website hosting companies. The only problem is, I don't have a clue as to how they do it! I mean, I know how to implement code via a SSI line, but that line can easily be erased. I assume to accomplish this task I would need to add something to my htaccess file, but I am not quite sure what will to that. Does anyone have any ideas as to how to do this?
I appreciate anyones help!
~Kyle

[Kaisa]

1) A few banners (Some people hate seeing the same banner !)
2)Pop-Up menu script
3)Random banner script (Might be called circleing banner etc.)
4)A script where you can make people not edit the banner like a view source edit killer !

i found the script for the banner on my own maybe you can find one on Webdeveloper.com :D