Are you hoping for twins, or a singleton? I kind of love the idea of twins, but in reality it would be pretty overwhelming!
If you click on "Go Advanced" under the little reply window, and look at all the icons along the top of the reply box, there's a little paperclip. Clicking the paperclip opens a new window for uploading. You select your photo using the button on the top left (I think it says Choose Photo or something), then scroll all the way to the right and hit the button there (I think it says Upload). Once it's uploaded, you close that page, and when you post your photo will come up.
You can also post it on an image sharing site like Photobucket, and post the IMG link, but that's a little more complicated.