There's an app for that, but unfortunately I don't have my laptop with me, but in moments like this, just remember, Google is your friend!
Sent From My HTC G2 Which Lives On!
and again, photoshop does the best multiple photo resizing... u can just do 10k of pics resizing in one click....
watch the tutorial in here
http://www.youtube.com/watch?v=pBXB9I4DlpE