Steam Activate Key

Hello.
I'm makig keygen for steam.

Now I'm using:
in order to type in key and submit it.

But seam activation window has to be the active one and I can't do anything on my PC. Because as soon as that steam window looses focus it all gets messad up.

I have two questions.

1.) How can I send keystrokes to backgrouns application in C#?

2.) Is there any other way to implement that keygen?
For example calling some function from injected dll?