I recently experienced some unusual behavior in using a 3rd party Navigator component in Delphi 2007 whereby upon setting the 'Flat' property to True, the buttons didn't remain Flat as they should with Themes Enabled but did so once I unchecked Enable Themes from within my project file and recompiled my program. This obviously didn't seem right since another 3rd party Navigator component I experimented with performed accordingly with 'Flat' set to True and Themes Enabled. I then tried the same with Delphi's TDBNavigator and once again I experienced the same problem as I did with the first 3rd party Navigator component. In researching this matter online, I have found very little other than the fact that, unlike previous versions of Delphi, Delphi 2007 supports Themed Applications out of the box as opposed to having to add another component to support WinXP Themes. All considered, I am hoping that someone else may have experienced similar problems in using TDBNavigator or other 3rd party Navigator components in Themed Applications with the flat property set to true. Any comments or suggestions regarding this matter are appreciated.
Theme support was added to Delphi 2007, but doesn't apply to 100% of the VCL (grids, for example, don't have theme support). I'd suspect that's the issue you're having with the TDBNavigator.
As far as your "3rd party Navigator" problems, it's impossible to give you any advice because you didn't indicate which "3rd party Navigator" controls you're using. Without knowing the specific component names, you've given no information to us to use in trying to help.
Delphi 2010 provides full theme support, including grids. I haven't tested the DBNavigator, as I haven't used it since Delphi 2 or so. Note, however, that Delphi 2009/2010 introduces other issues with older code, because as of Delphi 2009 the VCL is Unicode-based. Some code that uses strings and assumes that a Char is 1 byte in size can be an issue.