I am not sold on the color selections, but I think this tab approach would be helpful for the sub-sites. The tabs would carry through the subs and users would be able to see which site they were on.
Also I didn't work it into the mock-up but I really think the user login and then user info should be part of the header also, rather than using up valuable side-block space.
Here is the mock-up:
http://www.bigreactor.net/images/header.gif
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