Hi Tomas - I presume the quoted comment is referring to the "bitmap" option discussed on this page:
http://help.adobe.com/en_US/photoshop/cs/using/WSfd1234e1c4b69f30ea53e41001031ab64-73d6a.html
There are many, many options / variables when one does such a conversion, e.g., see the previous URL, as well as the two attached screen grabs. When you speak to the printer, you need to find out *EXACTLY* which settings/options they require.
That being said, I am astonished that they are asking you to do that conversion. If you present any competent printer with an AI file, and EPS file, or even a PS file in RGB 16 bpc mode that contains only black and white areas, it should be absolutely trivial for them to do the conversion, and do so exactly the way that is optimized for their particular process.
As an example, in the newspaper industry, where all photos used to be produced by a half-tone screen method, the photographers would NEVER get involved in the conversion of the photograph to half-tone. The technicians at the print shop would always handle this in the best way for their particular press.
Because of this, I'm starting to wonder if you aren't getting some bad advice from them, or possibly you are speaking to the wrong person at their shop.
HTH,
Tom
PS - Note that the discussion in this post about the conversion of a conventional RGB or grayscale image to Photoshop's "bitmap" image mode is entirely distinct from our previous discussion of tracing accuracy, the minimum ppi one should use when rendering vector graphics, etc. If your printer insists that you set the conversion options yourself, you probably should read some articles that discuss the difference between ppi and line screen frequencies before you talk to them again, e.g., http://web.sos.com.au/index.php/dpi-vs-lpi.html. Another possibility (as suggested by ALB, above) is to check out other print shops.