lucy24 - 11:30 pm on Mar 3, 2013 (gmt 0)
If I'm reading your first post correctly, the two domains live in different places-- different physical servers, even --so requests for Old Blog and requests for New Blog will never set eyes on each other. This simplifies things a lot.
The one thing you don't say is where your attempted redirects are located. If they are anywhere other than the old site's htaccess, requests will never see them so they can have no effect.
A Redirect by that name will not work. You can use RedirectMatch if and only if the old site does not use mod_rewrite at all. If it does, you will have to make your redirect using mod_rewrite. But that's trivial.
The most important thing is getting the redirect rule in the right location.
:: pause here to admire the way everyone is sitting on their hands w/r/t the "redirect everything to home page" aspect ;) ::