Go and download it right now! It's pretty easy to use, and sooo much easier than messing around with a breadboard. Very useful and powerful software, loads of help and tutorials out there.
A few quirks and limitations, most of the opamp and comparator models are Linear Tech devices, but you can find other ones online if you need them. To start with, I just pick any old device from the list and see if it works. I swapped your LM339 for an LT1017 and just ran with it, seems to give sensible results.
Give it a try!