batch file renaming in windows xp?

So for some reason my mp3 ripping program put a .wav file extension on some of the songs that I ripped. But they're definitely mp3 files because of the size and the fact that if you just rename them with a .mp3 extension they work just fine. So I'm wondering if I can change the file extension on a whole batch of files or if I have to do each one individually. Any help here would be great as I don't relish the thought of renaming a few hundred files.

Oldschool DOS way:
ren *.wav *.mp3

Longer explantion:
Start -> Run... -> cmd
Navigate to the directory/folder containing your files.
ren *.wav *.mp3
exit

Just make sure you don't have any true WAVs in there when you run the ren.

There must be a better way, but I don't know of one.

I use a program called ARen Batch Renamer
http://aren.hulubulu.dk/

thanks for the help guys. much appreciated.:D