Start a reply by clicking on the Go Advanced button. Scroll down when the reply screen appears and find the Manage Attachments button.
A window with the same title appears when you click that button (you must disable your pop-up blocking software first). Use the Browse button to navigate to the file you want to upload. Do Upload, then Close Window.
You are back at the reply form, and should have your file(s) listed on the bottom in the [i]Attach Files[/i] section. You can do [i]Submit Reply[/i] now. Your post should look something [like this](http://member.newsguy.com/%7Ewindoze/files/Image3.jpg), possibly not as pretty but it takes time and practice to make good-looking posts =). You have 30 minutes to correct any errors by editing the post, it will be automatically locked afterwards.