This is a great question. We would definitely encourage you to post free designs to our forums, making sure that you name the forum post appropriately and tag the posts so that other users can easily find them. You should be able to attach the file to your forum post. We do have file size limits, so make sure that you zip the design file in order to make the upload as economical as possible.
Please see the following post for more details on searching for free designs that other users have contributed.
http://www.annthegran.com/cs/forums/p/183/340.aspx#340
If you would like to post a free design for others to use, please make sure that it is an original design that you have created yourself from non-licensed artwork. In other words, don't use something like a Disney character, because you did not create that character, or don't use Clip Art that is not licensed for general use.
To post a design, go to our General Discussion forum, and click on 'Write a New Post'. You will see a tab that says 'Options'. Click on it and then choose 'Add/Update' under File Attachment. Attach the file from your computer, create your message in the 'Compose' tab, add any appropriate tags (ie. Free Design), and save your post. An example of one that I have created as a general user is at:
http://www.annthegran.com/cs/forums/t/213.aspx
Please note that any designs that violate copyright or licensing guidelines will be removed immediately at our discretion.