You can go to: www.photobucket.com (register and everything, it's free) and upload pictures from your computer onto that site. Then, when you come here to post them, you will see a "img" button above the text space where you are typing. Click on that, then copy and paste the picture.jpg url right after that; then click it again. So before you submit that post, it should look like: [img] your-picture.jpg [/img] If the .jpg isn't on the end of the URL, it won't post as a pic, only the link to the pic. Good luck!
Do you have a photo gallery on this site? If so, you can just do exactly what I just told you, but from this site.