To attach files into your post, you must use the advanced reply box (not the little box at the bottom of the thread). Click on the "Go Advanced" button. Then type in your message, and click on the "Manage Attachments" button in the Additional Options section. This will pop up a window where you can browse and select a file on your hard disk. Once you get the file click on the "Upload" button and wait for the file to be uploaded. There is a space limitation that doesn't allow you to upload files if they are too large. Assuming your file uploaded correctly, the popup window will then update with a message telling you that your file was uploaded. Once this is done, close this window and submit your reply.
If you file is too large to be uploaded directly in the forum, you can put it on a website somewhere, and just post an URL (
http://www.yoursite.com/yourfile.zip) so that people can download it from there.
P.S. Also consider editing your posts instead of posting twice in a row
*edited*
P.P.S. This rather belongs to the waypointing forum in fact... moving it there, no objections ?