I have tried to make it somewhat version agnostic to make sure that it'd be as useful as possible for everyone. There are a few changes from the RAW. The Wild-Die instead of throwing botch-dice will keep rolling negative rolls downwards (easier to deal with from a LUA standapoint).
The combat tracker is going to get two alternative counts on it one with our houserules attatched (the current one) and one rules as written version choosable from the preferences. But truth to be told it is a work in progress in my rather sparse free time so it might be a while before it is brought entirely in line with the basic Ars Magica rules. I will try to supply a manual for it with the next release though.
Start your Fantasy Grounds launcher, click the Application Data folder, then drop the Arm.pak file into the rulesets sub directory.
Then just create a new campaig choosing Arm as the ruleset.