How to use modrewrite to redirect certain portions of a site

[apo11o177]

Hello!

My question is as follows:

Suppose there is SiteA which is a blog that has a url structure of http://www.siteA.com/blog/category/article

Now suppose I'd like to redirect those articles to a new domain (which has the same url structure) BUT excluding a certain category, say, 'blah/'

so in other words, some examples:

http://www.siteA.com/blog/shoes/best-shoes-to-buy ->redirects-> http://www.siteB.com/blog/shoes/best-shoes-to-buy/ (there is a trailing slash here for some reason)

BUT

http://www.siteA.com/blog/blah/foo-bar -NO REDIRECT- (because it's in the /blah/ category).

Any and all feedback & help would be much appreciated  Thanks!~