Step 1) "D:\WCU\SSE\SQLExpr32_x86_enu.exe" /q /ACTION=Install /FEATURES=SQL /INSTANCENAME=SQLEXPRESS /SQLSVCACCOUNT="NT AUTHORITY\Network Service" /SQLSVCStartupType=Automatic /AddCurrentUserAsSqlAdmin /ENABLERANU=1 /SKIPRULES=RebootRequiredCheck /hideconsole /TIMESTAMP="VSExpress_10.0"

Recommended: copy and paste into cmd.exe environment

step 2) while it is still installing background, open taskmgr.exe, monitor the process SQLxxx in the list

Suggestion: when SQLxxx is not shown in the list, it means the silent install fails to work, then check out SQL error log in Temp directory; e.g. missing Windows Installer 4.5


step 3) when these two program services (sqlservr.exe, sqlwriter.exe) running, the installer has finished its task

Suggestion: please wait until setup100.exe process in the task manager disappears

step 4) open cmd.exe, and type: osql -S .\sqlexpress -E
1> print @@version
2> go

>>> Microsoft SQL Server 2008 (SP1) - 10.0.2531.0
Express Edition...

Suggestion: the above step no. 4 can be used to verify for SQL Server 2005 Express


The above steps works for my XP SP2 too!