Bulk Rename Utility is a very usefull program if you need to rename a lot of files. It supports
Regular Experssions, so you can do some very powerful tricks with it.
Windows Powershell is a little advertised part of the .NET architecture, natively inside Windows Vista and 7 but also available for XP as a download.
The reason why you'd be interested in it, is that it's a lot more capable shell for Windows than the regular command prompt and allows writing complex scripts comparable to what you'd find on Linux bash or perl shells possible. It also supports Regular Experssions.