If you have a MegaGames account (create an account here), you can contribute through your account profile page. Click on the 'Add new game content' link (see image below) to load up the form.
The following list of content can be submitted: Trainers, Fixes, Mods, Cheats, Freeware, Emulators, News, Patches, Demos, Videos
After you submit your content, it will go through our review process by the editors. You will be able to check the status of your contribution under the 'game contributions workbench' area on your account profile page:
If we require any additional information regarding your contribution, we will contact you through the email address listed on your account. You will receive full credit for your contribution.