I'm not sure why you want to send them a sample chapter rather than have a page on the site where they can read one. This is what sites like Amazon do. Many people are leery of giving out their e-mail address for fear of spam. Also people are used to instant gratification on the web and asking them to wait for an e-mail will lose you a lot of sales. I would advise you to make a graphic (say a picture of the book cover) with something like "Sample Chapter!" written over it, put it in a prominent place on the home page and make the graphic link to a page that contains the sample. The sample page can be very basic and still do the job.