The short question is how do I set my custom theme as the default theme?

Here's more detail:

Several places have said to set the following registry key:
\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeWeb\OWA\Themes\DefaultTheme
(http://technet.microsoft.com/en-us/library/aa996029.aspx)

I have not been able to get this to work, even with the themes that ship
with Exchange.

Does anyone have specific ID's that they've gotten to work in the two
registry values?  (one ID for the custom theme, and the corresponding ID for
the Default theme setting)

Abandoning this route I tried copying my default theme overwriting the MS
default theme, located here:
C:\Program Files\Exchsrvr\exchweb\themes\0
This still resulted in a problem.  The page background color of: #2557ad is
still visable.  I think this is a frameset color which cannot be set via CSS.
This value is set here for custom themes:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeWeb\OWA\Themes\[Themename]
Value: id=[ID];path=[PATH];title=[Title];bgcolor=[HEXCOLOR]
...the location to change this for the default theme cannot be found.

Oh guru please help.

I have been able to change themes, but I didn't use that document.  I
suggest you Google "Exchange 2003 OWA Themes" and compare the notes of
others with that reference.  Perhaps you're missing a step, or the document
misses a step.
--
Ed Crowley
MVP - Exchange

Here are good registry values that I've tested and should work for anyone who
finds this article:

Your Custom theme registry value goes here
\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeWeb\OWA\Themes\[YourCustomThemeName]
id=100;path=[Path];title=[Title];bgcolor=[bgcolor]

Add a Dword value here named 'DefaultTheme':
\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeWeb\OWA\
Set the Hex Value to 0x80000064

It apears that I'm the guru.  After much searching I was able to hack OWA
2003 to get my custom theme set as the default.

This technet article:
http://technet.microsoft.com/en-us/library/aa996029.aspx has a mistake which
was part of the problem.  The DWord value named DefaultTheme goes here:

\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeWeb\OWA\
not here (as mentioned in the article):
\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeWeb\OWA\Themes\

Once you create this registry entry you then need to OR the id you set in
your custom theme with 0x80000000

I used the online HEX calculator here to do it:
http://www.squarebox.co.uk/hcalc.html

Thanks me, you rock!