Confused as to why the installation of SQL Server Express 2008 has been so troublesome

I am trying to install Sql Server Express 2008 and I've been having trouble doing this simple procedure.  Why?  Who did this procedure and why is it so ridiculously complicated?  My problem started because I need to install Sql Server Express 2008 on drive D.  I just modified the path displayed to the D: drive (as opposed to C:).  The rest of the path was untouched.  So it created this string: "D:\Program Files (x86)\Microsoft SQL Server\"  (omit the "" quotes).  Unfortunately, it did not go as planned.  The setup generated an error: "The INSTALLSHAREDDIR command line value was not specified.  This value must be specified when the INSTALLSHAREDWOWDIR command line value is specified ".  So this simple task was starting to get unnecessarily complicated.  I then specified the command line: & ...