The good news is that it appears to be easy. The bad news is that like me you will not be allowed to do it for a while. I tried a few days ago, and it told me that I had not made enough posts to qualify. You have about as many posts as I do, so you are probably in the same boat.
Use screen print and paint to capture the pic, then upload it to a picture service that will provide a url, then put it in the post. very simple really, but we cant do it yet. DRAT!
You can post it through documents. If you use imageshack go to documents and select the file. Copy and paste the IMG ( forum hotlink it may be called )here.