Thank-you Okke for your 2 responses. I hate to be unappreciative, but I think that I actually need is something even simpler, but more importantly, unless I'm doing something wrong with your file, I need there to be nothing at all before the first image appears. So let me be a little more clear. It seems that your settings have the # "0" at the first frame, and then the # "1" at frame 30, #2 at frame 60 etc. And I think I get what you did there, but the problem is that I don't want anything at all until say frame 30 ( I assume as a workaround in this case that I could probably animate the font size so that it's zero until I want to see it). And then I only want #1. I would use a second set of tools to start another image at say frame 42, etc with entirely arbitrary different frame starts. Does this make sense?
some minutes later...
So with the help of your settings I figured out what's going on. One can't animate x and y density -and get any effect at all- unless you have "create particles every frame" checked on. And then you have to animate from 0 to say .1 and back to 0 over 3 frames. So in a sense, thanx to you, I have solved my own problem. But since I have your attention... if you're able to write me a little script that does that for any arbitrary frame that I pick it sure would make my life easier
I frankly don't know anything about scripting. I'm guessing that changing the %30 to something else30 would do the job, but I don't know what that something else should be.
Thanx so much to all of you who responded.