For pictures, I would recommend using imgur.  Go to http://www.imgur.com and follow the instructions.  They make it ridiculously easy to post pictures.  After you post the picture, they will give you a link address for the picture.  What you want to do then is click on the little button that looks like a picture when you are writing a post here.  It will insert tags that look like this:
[img][/img]

Paste the link address between those two takes like this:
[img]http://www.imgur.com/blahblah[/img]

For video, it's a little more involved.  You'll need to create a youtube account - http://www.youtube.com.  Then, follow the directions to upload the video.  Once it's uploaded, you'll get a link address, similar to that from imgur.  You can just paste that link into the forum post and people can click on it to watch your movie.