Have you uploaded your pictures to 'Image Shack' (with a space between the words) or to 'ImageShack'. The former is a UK site, dedicated to selling the works of photographers. It doesn't offer the facility you're seeking. The latter is a US site which does what you want.
Assuming that you've found the right site, take a look at this doggy pic:
http://img14.imageshack.us/i/setter1.jpg/
To include it in a forum (which accepts embedded pictures), click on the link next to 'Forum' and then right-click and select 'Copy' (Or use Ctrl-C). Where you want the picture to appear within a forum, right-click and select 'Paste' (or use Ctrl-V).
If the forum doesn't accept embedded pictures you'll have to post a link to the picture, using a technique similar to the one above. Choose 'Link' if you want the viewer to see an ImageShack page, like this:
http://yfrog.com/0esetter1j
Choose 'Direct' if you only want them to see the picture, like this:
http://img14.imagesha...img14/118/setter1.jpg
Chris