<p>I have an have an ASP.Net page which contains a button. This Page contains a ServerSide Paypal button.</p>

<p>When pushed my server does various clever things on the back end and then rewrites the response as a form and some javascript which posts this form to paypal..</p>

<p>This all works great.</p>

<p>However, if the user then elects to click back, they will arrive at my generated self-posting form and that will forward them again to Paypal. </p>

<p>I thought if I could find a way to have my generated form page not exist in the history, then this will solve my problem. but I have no idea how to correct this.</p>

<p><strong>How can I remove my page from the history or just have it never appear?</strong></p>

<p>Update: Thanks to all... Those are some great answers. Upvoted all good ones but went with splattne on account of clever use of hidden field rather than cookies for basis of decision.</p>

As a web application, you'll never have full control of the user's browser.  Even if there was a way to instruct the browser to not store the page in history, which I doubt, you can't be sure it'll work.  For example, a clever user could tweak an open-source browser to store every page in history, no matter what.
I think you should try to approach the problem from another angle.  You could, for example, detect that it's the same form which is being forwarded and not send it to paypal the second time.  The important thing is to do it server-side.