There is a 2D demo. Should be included in the package.
The reason it is more complex is because it piggybacks on the 3D effects and renders them to 2D textures you can use on sprites.
Here are the important bits from the 2D demo: (the effect is set to invisible so that the actual 3D effect doesn't show up in the cam view. The 2D render function will toggle it on and back off automatically for the render2texture.)
// Load an explosion effect, we will add this to the sprite texture
fxExplosion2 = gpup_loadEffect("explosion7_dirt", 0,0,0,1.0)
// prepare a texture for the fire effect to be rendered into. 256 is the pixel size of the tex.
imExplosion = gpup_addTex(256)
// Create a sprite that will display the effect
spExplosion = CreateSprite(imExplosion)
And then in the main loop
// Update the particle system. Call this every refresh.
// If the effect is additive blended, we must set the background to black for the capture
SetClearColor( 0, 0, 0 )
// Render the explosion into the cleared texture
gpup_effect2Tex(imExplosion, fxExplosion, 1)
Hope this helps you to get started with the 2D use of the effects.