It's also a good idea to check if a user has xLib on, that is possible with real(6), as without xLib that would return 6. With xlib it wouldn't return anything.
So put anywhere at the top of your program something like this:
if real(6)=6
then
disp "You need xLib
Stop
end

But if you want real power you should use DoorsCS instead of xLib, that gives you even more features for later on and it gives you a epic GUI and also allows you running archived programs from homescreen. It is found here: http://www.cemetech.net/programs/index.php?mode=file&path=/beta/dcs72b2.zip

DeepThought(calculateMeanOfLife);

Yep, and that other screen on the backup buffer you can copy to a image with real(9,2,<picnumber>), then you can clear the backup-buffer with real(0,0) and draw some new stuff to the backup-buffer, and then let the user see everything with real(6)

ok, first of all, with xLib you have two screens so to say.
One screen is the normal screen.
The other screen is some backup screen (screen buffer). Everything you draw onto the normal screen is also drawn to the backup buffer, but you can optional just write to the backup buffer, the user doesn't see this.
Remember the last parameter of drawing sprites being one so that it updates the screen? That is because xLib draws all the time to the backup buffer, with that being one you tell the calc to copy everything from the backup buffer to the normal screen. Leaving it 0 would just draw it to the backup buffer and you wouldn't see it on the screen.
You could also just do real(6) to copy everything from the backup buffer to the normal buffer.
Now, you could draw a lot of stuff into the backup buffer, store everything from the backup buffer into a pic, clear again the backup buffer, draw some other stuff there (e.g. a menu), and then update the LCD by e.g. using real(6) and so you have created the pics you need for sprites without that the user notices that!
I hope you get my explanation

Or maybe also exporting directly into a program, that would be cool!

Nope, full pics are 64*96 pixels
And you could make that when you start the program it creates the pics what the user doesn't see (by just using the backup buffer) and by exiting delete them so that the user has more RAM.
And yes, they'd need xLib (or DoorsCS which also has xLib included and is A LOT more awesome), but everyone should have DoorsCS anyways xD

Well, xlib supports all sprite lengths, the width just have to be dividable with 8, that's the limit.
And when I needed to make a nyan cat I took the animation from http://nyan.cat downloaded it, opened it with gimp and scaled it down, then copied pixel by pixel.