It's actually quite simple to post pictures in your posts, so let me see if I can help you out here. How I (and everybody else, I would assume) post them:
Step 1 - Upload your pictures to your Flickr or Brickshelf gallery
Step 2 (If using Brickshelf) - Click on your photo until it is all on its own on the empty white screen, and copy the URL at the top of the screen.
Step 2 (If using Flickr) - Click on your image, you should then see a button that says "all sizes" - click that, and on the next page you can copy the direct URL of the image from there. I prefer using Flickr, especially since they already provide you with various sizes of your photo (since you can't post huge images here on the forums).
Step 3 - Paste the URL in your post.
Step 4 - Highlight the URL, then click the "Img" button.
Knowing me, I was probably too vague or left out some info, so if you are still having trouble let me know and I'll correct myself.
Hope this helps!