I finally got SP1 visible to me on WU.

I have a Dell XPS M1530 (built Jan 2008) Vista Home Premium with an older version
of the SigmaTel Audio driver. Because my machine had an older version, WU did not make SP1
available to me and at the Dell driver download site for my XPS M1530, a newer one
was not represented either.

However, Chris (a Dell liason), mentioned that there was a new Dell driver download R171788 for the SigmaTel driver.
I used R171788 to do a search on the Dell Driver and Downloads website. I got to the download web page and
successfully downloaded the new Sigmatel driver.
But still no SP1 in WU.

So, I saw a one liner at a MS website (mentioned in one of Woody's messages on his main page) that
gave info on drivers that needed to be updated. It was buried at the end of the info and
said that SP1 would not become available until all MS security related updates were installed.

I was holding off on installing the latest OFFICE security patches shown in WU but per the
above one liner I installed:
Security Update for the 2007 Microsoft Office System (KB947801)
Security Update for Microsoft Office Excel 2007 (KB946974)

Service Pack 1 showed up in WU!