How to export a CMYK document to a black/white or greyscale pdf for print?

Question

Hello, I have some knowledge in graphics design, but very little about color management.
Currently I need to convert an instruction manual I made to black and white output only. We'd prefer to keep the indesign (.indd) and it's source images in their respective colors, but when exporting the document to a pdf my printer can use, we'd like to make that document a black and white pdf, as it's a black/white manual anyway. A little color conversion isn't to bad, as long as it's reasonable. all images that might give trouble are in greyscale anyway.
So how do I export a full color indesign document to a black&white/greyscale pdf?
ps:
very newb question, but if you don't ask, you never learn:
When do you use the colours "registration", and when do you use "paper"?

Answer 1

I am also trying desperately to convert my CMYK colors into a grayscale so that when I print the document the printer only uses K (and C=0 M=0 Y=0)
And I saw this bit of info you wrote a few months ago. I am working working with photoshop CS4. I tried to follow it but I found the following difficulties. Hope you don't mind me writing over your text.
RGB image --> Grayscale
New doc --> CMYK image,same size, empty
Copy Grayscale and paste into the K-channel of the CMYK image. - (It only allows me to copy onto the CMYK layer but not onto the Black so I had to Drag layer onto channel delete the black layer and rename my new layer as black but then the document changes from CMYK to Multichannel and I have to re-change the mode again to CMYK but this already prints CMYK...)
Place image in InDesign doc.
Everything else (vector, text) by K-only.
(...then when I placet that CMYK file into InDesign, and PDF it, on the output preview still separates the grayscale image into CMYK and when I print, the printer still prints CMYK instead of only K)
So then I say OK so.. let's use the Multichannel document instead, which it actually seems to print on K only (while CMY=0), it only allows me to save as PSD. and when I try to place it on Indesign... I have a message saying that this file is using an unsupported colour space, only RGB,CMYK, lab, indexed, and bitmap are supported by the photoshop filter
On top of that I have been asked for a Jpeg image in black and white which prints only K (while CMY=0). I have tried with channel mixed presets and even though the info on screen is now C=0, M=0, Y=0 and K= various values, when I send it to print. The printer still prints with all the CMYK colours
Any advice would be so much appreciated!
Thank you