Use a thumbnail program
http://www.thumbnailme.com/ for example to make a 6x6 thumbnail of your video's
Visit an image hosting site like imgchilli, imgdino, imagetwist etc, create an account and log in
Upload your thumbnail and get the BB Code link
Visit one of the approved file hosts - luckyshare, rapidgator etc, , create an account and log in
Upload your videos, and get the BB Code link
Create a new post, put the model name at the top, then put the thumbnail code below that, then put the video code below that, then underneath it all put the file type (mp4), length, size
Hit submit
Win!