holiday booking form

We need a holiday booking callender added to a site. We would be using holiday-bookings-online com which is an existing system which seems to work by placing some kind of iframe on the site (but we are open to any other sugestions if you already have a suitable system you know of or have used). The reason we are using this is that it allows off line payments by credit card which can be sent and manually entered into the offline credit card pricesiing machine as we dont want to taek payments online in the normal way So basically all you wil need to do is reskin the iframe type system mentioned above with css scripts and raw html etc to make the system mentioned integrated into the site using the system mentioned above and look as if totally integrated into the design of the site