Ignonimious- Are you finally starting a sketchbook thread? To answer you questions, just go to the top of the page in one of the forums, and right below "User CP" there should be an "Add Thread" button. Click it. Scroll down until you see "Additional Options." There should be a button there that says "Manage Attachments." Click it, and a new window comes up. Click the "Browse Button" to find the file in your computer that you want to upload. Once you find it, click the "Upload button." Repeat browsing and uploading until you have all the images that you want. Once you're done uploading images and typing your message, just click "Submit New Thread" and you're done!
To get back to the screen where you can upload images, you have to click the "Go Advanced" button bellow the Quick Reply box.