I've used imported letters from paint programs.  I had best results with high resolution in the paint program, import as a height map into Bryce terrain editor, smooth it , smooth it, make the terrain solid and clip the tops and base off to square it up.  You don't get the edge that a lattice creates.

Now some heresy, Hexagon can create some nice 3d lettering within the program and they can be exported to Bryce.