Select-String Pattern

Hello,

I have this script:

cls
$InetDrop = "c:\Temp"
$contains_stagingSP2010 = 	Get-childItem $InetDrop -filter *.eml -Recurse | `
							Select-String -Pattern ((' Staging *') -or (' SStaging *')) -AllMatches | `
							Select-Object Path,Filename
Write-Host $contains_stagingSP2010

In one of the files, there is the value Staging .Net included. but the result of my script is null.

How can i use -pattern with -or and -and ?

Thanks Horst MOSS 2007 Farm; MOSS 2010 Farm; TFS 2010; IIS 7.5