For Mudbox there are these tutorials put up just the other day by aphexx. The third one might be of particular interest to you. It's not the cleanest workflow for a tilable mesh but that's a problem with Mudbox not tutorial itself. Also this one over at the Area, using that method you can also crank up the opacity of the…
If you are using zbrush 3 then you can use the image plane plugin. There is a good video tutorial by Joseph Durst on the pixologic website showing how to use it to bake materials but you can use to grab all kinds of different maps. If you are using Zbrush 3.5 then you will have to wait for the plugin to be updated. Here is…
Actually there is an artist who made a tutorial on tileable textures in 2.5 and how to make a normal map with them too. here... http://vimeo.com/2228433
Sorry I'm of no help when it comes to Zbrush. Have you seen this tutorial by SHEPEIRO? The Polycount thread for it. It doesn't seem to be tileable sculpting so it may be of no use to you, but the end result is a tileable lowpoly + normal map and that's what you want right?