So, basically I wanted the customer to be able to input their name, address and how much they want to pay, and then pass these details to paypal ready for payment. Boy did I not realise how complicated this simple task would be.
Finally perfected it, so if you need to do this for your website here is the code to use:
<form action="https://www.paypal.com/cgi-bin/webscr" method="post">
<input type="hidden" name="cmd" value="_xclick">
<input type="hidden" name="business" value="YOUR_PAYPAL_EMAIL_ADDRESS">
<input type="hidden" name="on0" value="Customer Name">
<input type="hidden" name="on1" value="Customer Address">
Name:<br>
<input type="text" name="os0" /><br>
Address:<br>
<input type="text" name="os1" /><br>
Amount to pay (£):<br>
<input type="text" name="amount" />
<input type="hidden" name="item_name" value="Window Cleaning" />
<input type="hidden" name="no_shipping" value="0" />
<input type="hidden" name="no_note" value="1" />
<input type="hidden" name="currency_code" value="GBP" />
<br />
<input name="submit" type="submit" value="Pay Now" />
</form>
So, just thought some on here might find it useful. Feel free to use it if you like - but change the "YOUR_PAYPAL_EMAIL_ADDRESS" to your own, obviously!
May save you a few hours!