First of all, I know 2.0 is (somewhat) obsolete, and that there's a 3.0 in the beta stages. However, I would prefer to avoid 3.0, because it's too complex compared to 2.0.

In 2.0, the process was simple; input/import the parameters, 'create particle system', and you see the particles in action.

How about in 3.0? What if I don't have an .RMF file on-hand? Is there a way to make it work like 2.0, or better yet, a way to make 2.0 work properly?

2.0 aint obsolete... matter of fact every single NS player I know IRL plays 2.0. anyway, I can't help ya with teh NSPSEdit, as I am a swarthy QuArK user and it is uncompatible. A pity.

I believe he's referring to NSPSEdit when he mentions 2.0/3.0. 2.0 is not just obsolete - it was written without access to the NS particle code, so much of it is not-quite-right (particle aging), poorly named (Box2), and just plain wrong (Base colour). There's no way to make 2.0 work properly without re-writing it completely. The easiest way to do what you want is to make an RMF containing only an env_particles_custom entity (with maybe a brush or two for reference), and always use that for PS editing.

Oh, I forgot to mention that the sprites weren't showing up in 2.0.

I got down to making a simple .RMF for testing in 3.0, but the sprites still don't show up. The system is active, and is reportedly generating particles (hundreds of them), but I don't actually see any. Perhaps related to the issue that some (most?) people had when 2.0 was released. Has there been a solution to this?

No solution, I'm afraid. I've been unable to duplicate the problem, and other things have been taking up my time so there's been very little progress on NSPSEdit.