Changing the address the searchform returns…

This is probably a horrendously simple question, but I need to ask it nonetheless. I have a search bar on my site that is part of the wordpress installation. It works perfectly in the blog (which is in a subfolder (/blog/) and returns search queries at http://www.mohoyt.com/blog/index.php?s=search
However I also have the main index page for my site in a root folder that uses the WP header files and as a result also contains the search bar. When I search with this though, it returns
http://www.mohoyt.com/index.php?s=search
which returns nothing – just the homepage again.

How do I edit the searchform to get the /blog/ bit in the query return address?

Thanks very much.