I think the information here might be a good start for you. Heather
usually does some very decent customization docs:

www.heathersolomon.com/blog/articles/sp2007.aspx

My followup question  would be: Are there addition .master
templates/themes available for MOSS 2007?

Either for purchase or somewhere out there in the ether?

It would be awfully nice to not have to start developing this from
scratch or using a design tool I'm not familiar with.

There are aftermarket web parts... what about themes and templates
(.css / .master)?

As a new MOSS 2007 SharePoint Admin, I'm currently involved in
testing a MOSS 2007 deployment.

Part of that has been playing around with the in place upgrade
option. Since we had a plain vanilla installation of 2003, it seems
to be working well in the test environment.

However, the options for the Welcome Page (System Master Page / Site
Master Page) and the Site Themes are somewhat limited. I'm wonder
if anyone out there can point me to some source for System Master
Page replacement themes?

It would be a lot easier to do the initial customization using a
theme / CSS replacement initially, and then spend some development
time later prettying things up.

Any thoughts or direction on this matter would be greatly
appreciated.

I tried to answer this for you yesterday. If you look for message
Nr. 16429 you will see what I wrote. Also, instead of adding a new
post with the same question, just take your old post and add a reply
to it. This will move it up again to the top of the list :)

I'll take a look at the other post. Basically, the original message
I submitted never showed up in the listserve, and I assumed it was
never posted.