With the release of the SQL Server 2008 R2 November CTP, we have simplified the SQL Server Express (all editions and package) installation process.  In this release, we have completed the following:

  1. Reduced the number of clicks by 50% when performing an install.
  2. All inputs are defaulted on Vista and above operating systems.  (many inputs are defaults on Windows XP and Windows 2003, except for the service accounts)
  3. Skip (auto advance) through the UI, meaning non-essential dialogs will still be skipped.
  4. Reduced the size of the Express basic package

See http://blogs.msdn.com/petersad/archive/2009/11/13/how-to-install-sql-server-2008-r2-express-edition-november-ctp.aspx for step-by-step instructions on how to install.