Ok, here we go:
I have a picture called cow.jpg on my desktop. I've clicked on tinypic.com and uploaded it. I get given a message:
Thanks! We Got Your Image!
View Full Size Image
Click to add Tags...
HTML for Websites
[INPUT BOX]
IMG Code for Forums & Message Boards
[INPUT BOX]
URL for E-Mail & IM
[INPUT BOX]
Direct Link for Layouts
[INPUT BOX]
What I do next is click the input box beneath the "IMG Code for Forums & Message Boards" line. It should turn blue - the text is now selected.
On your keyboard, hold the CTRL key (bottom left) and hit the C key. This will "copy" the text.
Now come into this forum and reply to this thread as you have been doing. Type in the text box as usual, but before you hit submit, hold the CTRL key again and hit V. This will "paste" the text. Now when you hit submit, all those funny [ img ] tags and the URL in between them get converted by the forum into your picture. Hope that helps!