I'm also Vista-challenged! It took me a few tries also but what I finally figured out: go to the FWS site that you want to post on, type your message, click Add New Attachment, click browse and go to the pic you want and click on it. Then you have to wait. I thought it was instant but it takes awhile to load.
I hope this helps and I hope I made sense; I think this is what Lindyline was saying too--you have to be patient (which I'm usually not LOL)
Good luck-let me know if this works. (I'm ok with a computer but certainly not an expert!)