Picture posting 101:
1. click
http://www.imageshack.us/
2. click the Browse button and find the image file on your computer.
3. Double-click the image file (or click it and select "OK"). You'll then be back at the section shown above. Check the box to resize image if the original is very large, then click the Host It button.
4. You'll be taken to a window that looks like this:
4a. Click to highlight the contents of the bottom one ("Direct link to image"), right-click that highlighted text and select "copy".
5. Come back to your post on the forum, click the little
icon directly above where your typed message is going, and in the mini-window that pops up, right-click in the text box and select "paste", then [OK] button.
That's all there is to it.
When you get comfortable with that, you may start experimenting with the other options here:
Allowing a direct cut/paste into your message, or nifty thumbnail link to full-size image (helpful for a series of pic's or big ones), etc.
Cheers,
-HiAmp