Digital Scrapbooking - How do I do a double page spread?

[Sweet Pea UK]

I need to do a double page spread for uploading to a Photobook on the internet. The site that I am using does not seem to have a 12x12 page that spreads over 2 pages - I will need to do 2 separate pages.

My question is how do I make the pages look like they are joined together - i.e. if I have a photo that is right in the middle of the 2 pages??

I would really appreciate any help. Thanks x