My humble and not-so-informed answers:
When you post a pic and want to make it smaller, reduce the dimensions in ratio. For example: < img src="
http://www.yadayada.com/photo1.jpg" width=500 height=250> If you reduce the photo 1/5, you would make the dimensions width=400 height=200. A 2/5 reduction would be width=300 height=150, etc.
No, not any jpg can be used for a border - it has to be a tiled background....one that will replicate itself over and over to fill the dimensions you give it.
I will defer the third question to Billie (actually all three questions in case I've made an error in my answers).