Screen capture fastest way?

I'm not familiar with the different systems yet.
I believe it's possible with:
- Direct X
- Simulating a print screen button press
- API call
- Maybe some other way???
Now my question is which one's the fastest? Could someone supply me with a source code example for this pls?

Thx for helping this Noobie kid out...

Sorry wasn't paying attention! Didn't notice that I was in the maths forum! My excuses!

But in answer to your question:

BitBlt GetDC(GetDesktopWindow)

will do it, if you fill in the gaps.