Advertising Roadblocks?

Not sure if this is the most appropriate forum section for this, but since I assume it's done via a script, well...

My question is I've been seeing with increasing frequency, commercial sites using some sort of script that forces a redirect to an intermediary page which includes an advertisement before forwarding a person along to the page they requested. From what I can tell it probably uses some sort of htaccess rewrite and cookie combination so that in most cases, a user only see it once per day. Ideally I'd love to have some sort of control over it. Anyhow, by now I assume it's been made into a commercial ad script of some sort. Does anyone have any ideas about any that exist, or where I might find additional info.

Thanks for the help...

Like you said, this is probably done using a client-side language. It's a relatively simple thing to do.

When a user goes to a page that you want to advertise before, check if they have seen the add yet. If so, let them see. If not, direct them to the add page and set that they've seen it.

Of course in practice it's a bit more complicated when it comes down to tracking where people have visited, adds they've seen, etc, but that's really up to you to figure out for your own needs.