Kit,
You may already know this, so forgive if I re-state it. A *.bat file is a dos batch file. Unless you're running a windoze emulator, it won't necessarily run on a Mac.
As with any firmware upgrade, read and follow instructions carefully/exactly/religiously. Otherwise you very well may end up with an expensive brick that needs some technical guru to recover.
It would be worth finding someone's pc to borrow, if that is the way the instructions are guiding you.
Joe,
Ruby is a pretty decent platform independent language that you can either download the source for or precompiled binaries for popular targets. You've probably already figured it out, but there is a ruby-lang dot org site where you can find most/all of what you need.