Under a post, you should see this: If you click 'Upload a File', you can add the .scn file to a thread.
But you dont have to post a new thread everytime you need to "Upload a File" - you can do it at the end of a post too (in case you didnt notice).
Thanks to all your help I was able to post a Mauve Manicure map .http://forums.cardhunter.com/threads/mauve-manticore-submission-thread.4544/page-8