Change DPI on many photos at once

I have over 100 photos that I want to change the DPI to 72 so that I can upload them to the internet. They are currently 1mb each. Is there a way to change them all at one time instead of individually. I have a few different photo programs to use including Photoshop CS.
I do want to keep my original photos the way they were taken.
Thanks for your help.

Batch filing will do this. Photoshop and irfanview, (two I use) will do this. I find that Irfanview has more options to do this than Photoshop does. In Irfanview, under the "File" menu, select Batch conversion/rename, then at the bottom of that window is a tick box/radio button, make sure there is a check mark in that box, and click the "Advanced Options" button. It will let you convert mass amounts of files, saving as .jpg and will also allow you to change dpi. I believe there is an option to keep originals intact. Do you have irfanview?

Thanks for the reply. I do not have Irfanview. I have located it and will give it a try.
Thanks again.

You're welcome, and since you never used Irfanview, I think you're going to like it. I use it a lot for many different image tasks and the best thing is, it's free. ;) Oh and make sure you get the plugins with it.