It can export (but not import) PMX, but it's missing support for much PMX mumbo-jumbo, thus you're going to need either PMXe or Blender if your computer can't handle PMXe or you don't want to go by the restrictive terms of PMXe.
Xismo is a modelling software made for MMDers. While Blender can't export to PMD/PMX as its' own, there is a really cool addon for it called blender_mmdtools (use the powroupi fork, it's really handy). The best software for the task would be either Blender or Xismo.