Hi Rory!
I hope this will help. As others have mentioned, Photobucket is a pretty good free site to use. I'm sure there are several others out there but it's the one I use. That being the case, I'll show you how to get your pictures from Photobucket onto the FSM forum. When you follow the steps below, it might be helpful if you have your FSM session up as well as your Photobucket session up, too.
Step 1: When you start a new post on the FSM forum, click on the "Insert Image" icon as circled below.
Step 2: When you click on the icon, an "Insert Image" window will appear. The area I've circled below in red is where you'll put the link to your picture in just a couple of seconds.
Step 3: Next, go to Photobucket and find the picture you wish to use. Next to it, you'll see several links you could use (Email & IM, Direct, etc). I use the "Direct" one. When you click in that field, you should get a brief message that'll flash up saying "Copied". If this doesn't happen, then simply highlight the code in the "Direct" field and copy it (Ctrl-C).
Step 4: Go back to your FSM session and then paste the code into the field which I circled in Step 2 above. Once you click the dark grey "Insert" button just below the code field, you'll see your picture pop into your post. Just pay attention to where your cursor is as the time because that's where your picture will end up.
Ta-DAAAAA!
I hope this helps! Let me know I need to explain stuff better.
Eric