You are required to be in the Developer group to start new threads in these categories.
You may join this group from your Profile
Regards Chemist
Right after you have submited your new wallpaper type
www.n900wallpapers.com/pending
on your browser and you will reach a page with all the newly submited wallpapers. click on the one that is yours and it will get you to its edit page. Click "submit changes" and your wallpaper will be featured in the newest wallpapers.