experiment - can I track this?

I have two web sites. Since my conversion is not to my liking I have decided on a little experiment.
I converted one (lesser visited site into a sales letter) with a back-page full site. (To support some legacy links and cached links) In other words the index page is only a sales page and the reader can go back to the "original site" by clicking on a link at the end of the sales page.

The reason for this is my doubts regarding the sales page versus informational site argument. Many sites pretend (must say rather poorly) to be informational and their whole message is bogus. Sometimes a pure sales site is more honest than a bogus "infomercial" type-site.
The question is besides the obvious argument I may be getting IS - how can I track this? My sales is done by 1shoppingcart (as well as my affiliate program)
I ask the shopper where he found me... but he/she is under obvious no obligation to answer. How can I tell what site a sales is made if I use an ASP?




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