PayPal buttons

I am developing a web site with DW CS3. This web site will sell herbs on-line.
Payments will be made via PayPal using their buttons.

Our requirements are that when a customer CLICKS the ?Add to Cart? button for
the first time, they are presented with a page with ?Terms & Conditions?. If
they ACCEPT, then proceed to PayPal and complete the transaction. If the
reject, they go back to the same page where they pressed the ?Add to Cart?
button.

The customer has to accept ?Terms & Conditions? one time during their Web
visit. The next time they CLICK the ?Add to Cart?, the system checks if they
have already accepted the ?Terms & Conditions? and then move on.

PayPal has the following code for their ?Add to Cart? button:

<form target="paypal" action="https://www.paypal.com/cgi-bin/webscr"
method="post">
<input type="image" src="images/btn_AddToCart-1_Up.gif" border="0"
name="submit" alt="Add to Cart" />
<img alt="" border="0" src="https://www.paypal.com/en_US/i/scr/pixel.gif"
width="1" height="1">
<input type="hidden" name="add" value="1">
<input type="hidden" name="cmd" value="_cart">
<input type="hidden" name="business" value="ybajwa (AT) gobrainstorm (DOT) net">
<input type="hidden" name="item_name" value="Shoo the Flu - Trial Size">
<input type="hidden" name="item_number" value="HAKSTFT">
<input type="hidden" name="amount" value="19.95">
<input type="hidden" name="no_shipping" value="2">
<input type="hidden" name="return"
value="http://www.firehealer.com/hak_list.html">
<input type="hidden" name="no_note" value="1">
<input type="hidden" name="currency_code" value="USD">
<input type="hidden" name="weight" value="1">
<input type="hidden" name="weight_unit2" value="lbs" />
<input type="hidden" name="lc" value="US">
<input type="hidden" name="bn" value="PP-ShopCartBF">
</form>


Can somebody suggest how can I intercept this code to force the customer to
accept or reject the ?Terms & Conditions??

I am pretty new to JAVA script!

Kirti