Modification of order page on shopping cart

HI there We have a shopping cart that we need to modify one page on. The page in question is final page before checkout. We require a tick box added to the page that the customer must tick in order to accept the terms and conditions of the site and proceed to checkout if the customer does not tick the box they should get an error message telling them to accept the [login to view URL] would not proceed until the box is ticked. Underneath the tick box should be a link to the terms and conditions that would open in a new window (if clicked) The asp.net website uses pages .aspx and is written in language C# source code the modification should not interfere with any other aspects of the website - it must do only as detailed above. we have a test site set up that we can test the code on. please bid sensibly - high bids will be deleted. we have set the hourly rate low to reduce the bids as this a very very simple and small project. this is a small task but we have lots more ongoing work for the correct freelancer.