I'm not sure what you mean by "recreate the tropic and subtropic latitudes." If your axial tilt is, say, 23 degrees then the tropics are by definition to 23 degrees north and south, e.g. Subtropics are from there to 30 or 35 degrees, by most definitions.
Placing lines of longitude and latitude is actually pretty easy if your map projection is equirectangular. You just count pixels and do some division. Or you can download G Projector (it's free), load your map in (assuming it is equirectangular, since G Projector only accepts that as input) and it will spit out images in almost any projection you can think of, including lines of latitude and longitude, if you like.
But if you mean climatology, well, that gets complex, not least because no one can really define what "subtropic" means. Reading the Wikipedia article on Koppen Climates might help, too, especially looking at the world climate map that is included. Though I personally think that maps of biomes rather than climate per se is probably more useful.
The short answer is that tropical climates tend to extend from the equator to 10 or 15 degrees, then there is usually a band af aridity to about 30 degrees- especially on west coasts- then temperate climates beyond that. (Mind you, "temperate" covers everything from the humid swamps of Georgia to the frozen taiga of central Siberia.) Tundra and other arctic climates usually start somewhere around 65-75 degrees. On west coasts there tends to be a small band of Mediterranean climates between the deserts and the temperate climates. The "subtropic" climates that you're talking about are probably east coasts between 20-35 degrees or so that aren't deserts.
Both sangi39 and myself are struggling through this process right now.
EDIT-- Fortuitously, Pixie is currently putting together a great tutorial on climate creation.
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