There are a couple of ways to post pix. The first is when you click 'post reply' there will be a button down on the lower portion of the screen that says 'manage attachments'. Click that and then browse. When you've successfully filled in the boxes with the pix you want to upload, it is important to click the 'upload' button and WAIT till it completes.
If you want to post pix without the size limitations of the MR server, then you'll have to use a picture hosting site, like Photobucket, to store your pix. Then just copy/paste the IMG tag to the MR site.