Register at photobucket.com - it's free - and upload some photos onto it. There's a 'browse' button, when you click it it opens up the files on your pc and you just double click the photo you want to save. Click 'submit' and the image is saved.
To post a pic in a post on DIS
You'll need to pages open for this bit.
Open up your message box on DIS and open Photobucket in a different window.
When you are in the Reply box there are some little boxes above. You need to click 'Insert Image' the little yellow box with a couple of mountain in it - a box pops up, just paste your image address into there.
Sumbit your message and hey presto!