I would like to print a map with a high resolution map with a 300 DPI or better. It seems all the maps I have made have a 72 dpi. I have Photoshop and have failed so far. Thanks.
For prototype and personal use quantities, use the SVG or PDF formats, which are in vector form and can be scaled to any resolution. (I’m not sure if any features in these vector formats use raster images. If they do, those features may have limited resolution.)
For production quantities, install your own rendering tool chain and customise it as appropriate.
Your user name suggests a business user of mapping, so you should be thinking in terms of the second option.
See http://wiki.openstreetmap.org/wiki/OSM_on_Paper as a first collection …
Read and browse the OSM wiki for more hints … or try http://help.osm.org and SEARCH for topics to your aims.