I have some PayPal Buy-it-now buttons on our site, which are basically FORM posts, and I would like to force my customers to explicitly agree to our terms & conditions after they've clicked that button, before they get transported to PayPal.

So I was thinking that when they click on the BIN button, it should bring up a standards Windows-type box which contained a couple of our T&C's and once they clicked OK in that box, then they get redirected to PayPal.

How would I do that ?

are you using the paypal standard option?

Yes I am but also using other non-Paypal methods. I just used PayPal as an example to try and clarify what I was talking about.