Bill, which edition of SQL Server 2008 is your instance (that the SR1 installers can't see)? If it's the base model of Express, you'll need to update that to Express with Advanced Services (because AW2k8 requires iFTS and FILESTREAM that's not available in the base model).

Before I left SQLBU a couple weeks ago, I was working on updates to the SR2 installers. Since they haven't backfilled my old job yet, I'm still working on those in the moonlight, but the timeline's going to be longer than originally planned "Spring '09". If you're willing to try them out, the SR2 beta installers are up on CodePlex and are stable: they'll let you install only the databases that work on Express base model (or an instance that has iFTS or FILESTREAM disabled).