Hyperlinks

I'm designing my own website through iWeb and up till this evening it's been simplicity itself.

I'm copying much from my existing website which my friend made for me a couple of years ago but now I've come to total confusion.

On the website I'm copying I've got to Publications. On it there's a Buy Now button which has a link to Paypal and the items for purchase are all there.

I've gone to Paypal and found the code which I have copied using the HTML manager and although the URL shows up exactly the same, it's a completely different page, still Paypal but I get the welcome and sign up page.

What's happened and how do I fix it? It would be easier if I could show you the link but I've a feeling that's probably against the rules so I'd better not.

Please, can anyone help?