The faq says I need a copy of the original game. Okay, check. Then I need to make an ISO for it. I'm not sure my computer has the room. Then I need to burn it onto a CD. I have NEVER gotten hacked games to work on my Playstation. I have a device that "supposedly" lets me play them, but I never got it to work.
Your computer must have the room (about 550 MB) to hold the ISO long enough for you to patch it. The patch itself is 9.4 MB. The FAQ is very detailed in what you need to do with the patching program, which is available for download on the site or by googling it. Once patched, you have two options of playing the 1.3 ISO: Either you run on your computer with an emulator (such as EPSXE), or you burn the patched 1.3 ISO unto a CD for playing on your Playstation. I believe your PS1 will need to be modded for it to run modded ISO's such as 1.3.
Regarding your concern about Zodiac bosses being too easy, if you can get 1.3 working, you won't be dissapointed. The full version of this mod has made many, many, many people rage all over the internet (so much that I was convinced to generate an easier version of it, called 1.3 Content). You won't be dissapointed. And once you defeat those, there's always the 1.3 Deep Dungeon.