Network blog post appearing on my main site home page

Hi I have a network capable site. I have a blog on a subsite and i want to have those posts appear in the blog page of my main site (the home page) is this possible? Is there a plugin to make this possible? I see you have your tags plugin but i a) cant seem to get it tow work and b) i believe it would only add new posts. Do i need to change my main theme?