FarRiders and Iron Butt are 2 different organisations. FarRiders is Australian, Iron Butt is based in the USA but rides can be done worldwide. Both are about long-distance riding, Iron Butt being the most well-known with tougher rides.
FarRiders does have an interest in Iron Butt though, and if you do an Iron Butt ride in Oz you will also qualify for membership of FR.
Minimum ride for FR is 1000km, max 1200 in 24 hours - IB go from 1600km in 24 hrs to 16,000km in 10 days and some even more extreme rides.
No requirement to do more than 1 ride to become a member, once you get the number that's it.
Best thing is for you to look them up yourself, a simple google search brings up the links to the websites:
http://www.farriders.com/http://www.ironbutt.com/about/about.cfm
