Dear Fallout lovers,
I just downloaded "Fallout 3: Game Of The Year" by Steam, however I already played the Fallout 3 a couple years ago and I dont want to play it again.
Is it possible to play only the mods ???
If so, how can I do that on Stem ???
Thanks to any blessed soul that could light me in my ignorance.

Mods aren't standalone things you can just play on their own, they're integrated into the main game. So if you want to use them, you'll have to play the whole game again. I'm not sure why you would download the game if you didn't want to play it. As for how you would do it with Steam, I presume the same way you would do it with the disc version. There's a FAQ thread stickied to the top of the forum you probable should read.

You get a message popup for four of the expansions at the start of the game.

Those can be played at any time, I think you get a fast travel marker also.

The only one that can't be done separately is Broken Steel - that begins when your character completes the original main quest ending.

Expansions are not the same thing as mods. You don't play mods separately, they just become part of the main game. Unless you have one that adds a new area you can explore of course. Most are just enhancements/additions to the default game though. I'm not so sure about the fast travel markers though. I'm pretty sure there isn't one for Mothership Zeta until after you finish that quest, and you definitely don't get one for the Operation Anchorage or The Pitt. You need to find their locations first. Though I believe they will have a quest arrow you can follow if you select them.