hit Reply, and on the reply screen, you will see the Heading: Attach file: on the left hand side of the screen, just below 'Options'.

When you hit Browse, just browse to the folder that has your pictures in it. Select one of your pictures and then select "open"

When you are done with choosing your pictures, hit "Submit Reply" and you should be golden.

Most digital cameras shoot big pictures. You may want to download Infranview (it's freeware) so you can resize them.

You can find it here:
http://eoni.tucows.com/mmedia/adnload/194967_75076.html