1. Right click on the screenshots on the webiste that you store your pictures at
2. Click "Copy image URL"
3. Go to your topic and click "Paste"
4. Go into preview, highlight the link, and click the butten that looks like a picture
5. It should have something that has something like this *img* around the link. Post and watch your pic come!
EDIT: Oh, and if you want a good website to put your pictures on, try photo bucket or tiny-pic.