It appears you already figured out how to insert smileys. Inserting images is almost as easy. All you need is an image host, like
Nexuiz Ninjaz, for example. Choose the image/s you want to upload and click on "Start Uploading!". If the upload was successful, you should get some codes that you can use on websites or forums, like this one. Copy the appropriate code, in this case you should prefer the "Thumbnail for forums" code to save everyone's bandwidth.