You can't off your hard drive. You need to upload them to a web server somewhere (
www.webshots.com), then you click the "image" button on the bottom when you are posting, and put in the url to your picture.
Example:
[img]
www.mywebhosting.com/96gl.jpg [/img]
If you right click on the picture, then choose "properties" you will see the URL that I host pictures on.
Get it?