Post one post to two blogs on different sites

I have a client who wishes to have the same blog hosted in two places - on a dedicated blog site (site A), and on a blog on their main site (Site B). The idea is that a post would be made on Site A and then auto-posted to Site B.

How do I do this? Is it through setting up an RSS feed on Site A and then doing a feed import on Site B?

Thanks

Richard