Thunderbird. - no it does not look like office, but it works damn well.
I am afraid that you will have to bite the bullet on change and new user interfaces at some stage, staying with Office 2007 is not a long term option.
Personally I hated the Office 2007/2010 interface but eventually got used to it. When I recently had to use Office 2003 I realised how much I had adapted.
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