i want to stream videos and pictures through my pc and onto PS3 but cannot get it sussed

i run vista and have the latest media player on my pc then click on libary, down onto media sharing then dont really know where to go from there

looked on youtube and it shows this
http://www.youtube.com/watch?v=dJBT_...eature=related

but i dont get the same screen when click on media sharing, mine dosent say anything about unknown device just a box with "other users of this PC" and no windows symbol on my PS3

I'm crap with computers lol