Particle illusion has a built in limit of rendering to the largest screen size you can display (allowing for the menu bar) but there's a companion program that ships with it that can render separately at most any size, including 1920x1080. It only supports square pixels, but if you're using strict HD at 24 fps progressive, your pixels should be square in your rendering anyway. You can import footage to use as a reference, but I find that it works better if your reference footage is lower resolution. Once you've got the particles looking good, you can get rid of the background and composite separately (I use After Effects for that).

PI can render to file formats that support transparent backgrounds, and the newest versions can render to video formats that support it (such as AVI with the Lagarith codec). For clips of under ten seconds I usually render to AVI; if longer I usually render to PNG.

Those features are for the full package (version 3). The light, or SE package (version 2) has more limitations, and I haven't used it.

PI can also import position data from an external program, if you have it. For example, it's able to import position data from SynthEyes, and I once wrote a simple script (with some help on the math) for exporting position data from POV-Ray.

Generally, PI will work well for particle effects where the camera doesn't change rotation or zoom significantly. If you use a compisitong program you might be able to put the particle effects on a 3D layer and move it, but that might be problematic. Or, if Daz Studio supports it (I'm not familiar with it) you might be able to render a particle effect as a movie, then texture the movie onto a plane that always faces the camera.

PI comes with lots of particle emitters, and usually there are a new new free ones every month (there's been new releases of versions for use inside After Effects, and that's slowed down the delivery of free goodies a bit).

A really good resource for particle illusion is the forum at Creative Cow (free registration to post; click on "formums" and the link to the PI forum is on the right side about halfway down). Alan Lorence, the developer and driving force of PI, frequently steps in there to answer questions about the product directly, and there are other helpful folks there, too. Some nice tutorials there, too.