Im on 2.58. I cant seem to figure out how to key particles properties. I am trying to fade my particles based on particle lifetime.
hold your mouse cursor over the lifetime number slider and press the ‘I’ key to add a key frame to any property.
I think that just changes the lifetime, it doesnt drive a property from the lifetime.
In 2.5 the only way i know of is add a texture to the material your particles are using and set type to ’ Point Density’ then you can select particle life in the texture options to be a factor for the brightness/alpha of the particle.
So I played with the point density texture properties for the past hour or two, I cant seem to get it to work. 
Hi,
I think you might be after this…
There are other particle related overviews and tutorials on the blog too.
A blend texture set to use the colour ramp can be used to drive lifetime and alpha information as well as other attributes. Not just a blend texture either but that’s the simplest to control for most uses.
Hope that helps.
AidyB.
Ok, that did help a bit. However, as stated in the video, it seems like some aspects of the particle system still do not work.
2.58
Blender has also not provided success for me on the topic of
Particle alpha animation based on age / lifetime
If anyone knows of a explanation better than the video mentioned above
such info would be appreciated
Thanks