How to set the product posts in Recent listings?

Hello Mark,
I am newbie here, and I have some problems with recent listings on the home page.
I want to display only 12 listings on the home page but it displays 33+ listings.
I have set the recent listings object to display 12 posts per page ( add &posts_per_page=12 on query string), but it doesnt work. Then I also set the search listings to 12 posts per page. It works only for search listing page, but on the homepage it shows 33+ posts.
I try to add advanced search object, then it still displays 33+ listings.
How to fix it?
Thanks