There's some great info in here for people unfamiliar with posting pictures, especially Matt's post
here, which applies to pictures that are on the internet.
If you have a picture on your harddrive that you would like to post:
1. "Reply" to a post as usual.
2. Click on "Additional Options" below the Message screen.
3. Click on "Browse"
4. Select the picture from your hard drive
5. Click "Post"
This method only allows you to post picture(s) at the bottom of your reply as an attachment. If you want to put a pic from your hard drive in the middle of your post, you'll need to upload your photo to a picture-hosting website, such as
www.snapfish.com, which will produce a URL for the photo. You can then use the method that Matt described in the link above.