Halftone Effect

Hi brothers!

Its my first posting here and I am still very amateur in this photoshop area.
Anyone of you guys know how to create those Colour halftone effect??I had seen alot of advertising poster using those effects but i simply cant get to the way they did.
I tried the colour halftone in my PS 7 but its not what i want.
For example, I have an image of a face, Is there any way I can have this face to b seen as dots??
The Dots usually are spaced at different distances and in different sizes.
So from far, we can actually tell that its the face that we are portraying.
Really hope to do this effects!
Hoep you guys can help!

Select desired colors.Check out the filter>sketch>halftone pattern.

That should do it. If you decide not to use the dots, the best HT tool is the Image>adj>threshold. That should work.