here's how I do it.. Take your grayscale image in photoshop and convert to bitmap.. When you do this a window comes up asking you to set your output resolution size, ie 300 pixils per inch or what ever your output is desired..You may want to set this really high becasue bitmap file take less memory.. Immediatly below output resolution is METHOD.. Select halftone screen..Click OK then the "halftone screen" window pops up..Here you set lines per inch and also the angle you want your dots to flow.. The smaller the number on the linescreen option the bigger the dot..Set yer numbers and click OK and BOOM, you got a halftone bitmap file..
I'm looking to do a regular round dot halftone based on a greyscale photo. Usually I try the "halftone pattern" filter, but in order to get the contrast high enough, I end up darkening the whole image too much. I think I may be just skipping a step of something.
i prefer outputting all my images in quark. once there, you can select your line screen in your print dialogue windows.
also, if you only have photoshop, you can play with larger halftones by using the color halftone filter (it works perfectly on grayscale images.)