Welcome to Toyota Nation!
First thing you need to do is join a photo hosting service like
Photobucket, which is free.
After you join Photobucket you can upload your pictures from your computer to Photobucket. After the images are uploaded they will be assigned four links, EMail & IM, Direct Link, HTML tag, and IMG code.
Personally, I just right-click on the direct link which copies the URL to your computer's clipboard. Then, in a Toyota Nation reply click on the yellow Post An Image icon at the top of the text window (second from the right) and it will open a small window where you will paste the URL for your image. Click on Okay and then your photo will be posted.