You can do this in a couple of ways...BUT

By far the best way is to give something away using a squeeze page or splash page.

Trying to sell them something while they are busy surfing isn't the best use of traffic exchange page views.

Offering them a high quality report in exchange for their email address so you can tell them about your opportunity later via email is going to give you far better results.

To that end I would like to recommend a free service called Instant Squeeze Page generator, ISPG is an instant squeeze page wizard a simple point and click system that will create and host your squeeze pages, it even supplies all the free gifts you can use to tempt people onto your subscriber list