You create coordinate database by compiling coordinate list with coord_compile utility. Coordinate list is simply file in ASCII CSV (comma-separated values) format which specifies object's name and its X and Y coordinates. You can read details in coord_compile manual.
This howto page is however dedicated to tips and tricks on preparing coordinate list. There can be 2 choices:
For the first case, you both lucky and on your own: if you have database, you can save yourself lots of time by reusing it for MapMap instead of following somewhat tedious generic coordinate extraction procedure described below; however, noone can tell you how to do that in your case. So, let's assume that if you have existing coordinate info, and know that you in fact have it, then you also have an idea how to reuse it. Otherwise, you can always follow generic procedure anyway. Also, do not forget that there is a mailing list for MapMap users - ask there, maybe other users already had experience with format/data you have.
So, you can always just lookup object on a raster map, figure out its coordinates (which is as simple as pointing cursor at it and looking at statusbar/panel of your graphics editor), and write them by hand. I am working on making this all somehow more interactive, self-organizing, and thus, more productive and less tedious, but for now, graphics and word editors, Alt+Tab key, your eyes and hands are your best friends.
So, in Photoshop you open the map image, set suitable zoom, make sure that you have "Info" pane on screen (Window->Info checked), select Arrow tool (or any other which allows precise targetting), and do it.
Even at 3 objects per minute (I would bet for 5), you can transcribe 60 object in 20 minutes (at which point I guess you would want to switch to more enjoyable activity). Doing that once a day will allow you to build coordinate database for a big city (few thousand streets) in about a month. Do not do that (transcribing an entire city) yet though - better check with mailing lists if some new tips to speed up/optimize process are available. And do not forget that you can build database incrementally - just transcribe some objects of imemdiate intereset to you, compile it and put on your handheld. As you add more coordinates, you can recompile the list and put it on the run.