ScriptCenter has a couple chapters of Bruce Payette's awesome book:  Windows PowerShell in Action.  You can (and should) read part 2 of chapter 10 at:

http://www.microsoft.com/technet/scriptcenter/topics/winpsh/payette2.mspx

Part 2 focuses on file processing.

Enjoy

Jeffrey Snover [MSFT]
Windows PowerShell/MMC Architect
Visit the Windows PowerShell Team blog at:    http://blogs.msdn.com/PowerShell
Visit the Windows PowerShell ScriptCenter at:  http://www.microsoft.com/technet/scriptcenter/hubs/msh.mspx