Stevo, here's what you do:
Go to
www.imageshack.us
Hit Browse
Select your photo
Tick the 'resize image?' box, then scroll down to find 640x480 (for message boards)
Click Host it!
A page should appear that has a heap of different links for thumbnails, hotlinks, etc. Go straight to the bottom, and copy the URL from 'direct link to image'.
Once you get back to your thread reply, hit the little yellow button (next to the quote button) with what looks like a mountain on it. A box should appear that says 'please enter the url of your object'.
Delete the bit where it says 'http://', and paste the direct link into the box. Press ok.
You should be done!
Here's an example - this is a photo I took of the Crusade on the weekend...