Page slightly shifting and I don't know why?

I'm working on a site:

http://www.hsgsphoto.com/

when you click the entire page moves slightly when you go to the services link:

http://www.hsgsphoto.com/services.html

I've tried attaching the CSS file that is linked to the index page (main.css) to the services page (its currently linked to the main_services.css file) and the shifting is still going on so I'm kind of confused on what might be causing this. The main.css and main_services.css file are pretty much entirely the same other then a few extra rules for the text classes so I'm not sure why the page would be jumping like that and even more importantly I'm not sure what to do to stop it

Thanks for any feed back you can give

John

In main CSS for #header you have margin: 10px 0px 5px 0px;
In main_services.css you got margin: 10px 0px 10px 0px;
So change the 5px to 10px