Here, I'll help you :)
Gimme a sec to give you the Step-by-step how-to :P
Okay, this is what you should see when you begin to reply to a thread:
Now avert your attention to the red box.
See all those images? I want you to pay attention to the Globe.
And the Mountain.
Now, first click on the Mountain (Note: Have the image's URL in your Copy & Paste), then hit 'CTRL+V'
You should see something like '[IMG]URL[/*IMG]' without the *
Next copy the URL of where ever you want the image to take you.
Then drag your mouse over the '[IMG]URL[/*URL]' to select it, then click on the Globe and 'CTRL+V' to paste the link.
Finally, submit the post and TADA! You're done :)
Hope this helped :)