Although desktop inkjets use CMYK inks, they are RGB devices unless you have a Postscript RIP for them (in all but the highest end cases that's an additional purchase, often over $100 - sometimes way over). If you aren't aiming for commercial output you would probably be best sticking with RGB throughout (I do, with an Epson 1270 as my printer). In order to use CM you must have accurate profiles for your display and peripherals - those tell CM-aware software what actual colours your monitor or printer produces given a particular set of RGB (or CMYK for high-end printers) values, and what the RGB values your input devices report represent: canned profiles for your scanner and for the manufacturer's ink and paper may be better than nothing (I hope) and there are free software calibrators such as Adobe Gamma (included with Photoshop) which will at least get somewhere close. With most current software you pick a working space, which like the profiles specifies a relationship between numbers and real colours, and the software sends the appropriate RGB/CMYK values to the output device to get a colour as close as possible to the desired value. Incidentally, Hoofdcommissaris, the point of embedding a profile is not to describe the output device, but rather to say what the designer wanted the colours to be - the printer should then work to match those colours as closely as possible. If you don't embed I assume you send some kind of hardcopy instead, otherwise the printer has to guess your intentions.