I need to create an effect for a miniature room of a light going on when the door is opened and off when it's closed using a battery operated christmas light. Much the same way a fridge or car door works.

So I am guessing you need a microswitch? Try looking for one at Mouser Electronics - Electronic Component Distributor (http://www.mouser.com).

I put an alarm on my door when I was a kid. You can create an easy switch with some padding and tinfoil and put tinfoil on the door and the padded bit on the frame along the hinge side, so the contact is broken when the door is opened.

Or if you don't want to go the messy homemade way you can use a microswitch, which is pushed in when the door closes. (most fridges use this) I have one of these controlling the light in the cupboard under my stairs too.

Mouser is great for obscure or specialty items, but your local Radio Shack has a wide verity of micro switches and other momentary switches in both normally open and closed.