Hope this helps HM
1) Make sure the photo is less than 128Kb in size - this is done by resizing in your photo in your photo editing programme.
2) After you've written your post, click 'additional options' you get a box with 'browse' - hit browse, locate the photo on your computer and just click it - it should load up automatically.
3) I always highlight and right click on the text then hit copy before I hit the post button - but this is just incase my photo's not the right size - if it's too big the message you've written gets lost and mine are usually quite long
4) Hit the post button and (hopefully) hey presto
Alternatively you can set up a 'flickr' account, put all your photo's on there and just post a link to them, but if it's just the 1 photo it's probably easier to follow the steps above.
Good luck & look forward to seeing it !