"Ring Main" refers to power wiring - the circuit make a complete circle so that power to a socket may come from two directions...
House wiring for lighting is usually a loop-in system where the power snakes from one ceiling rose to another with the last rose in the chain not linked further.
You have interrupted the power and or neutral to the ceiling roses that are not working.
A ceiling fitting typically needs 4 separate terminals - Earth - Live - Neutral - and Switched Live (to turn the light on and off).
This picture may help explain things...
http://www.flameport.com/electric/lighting_circuits/lighting_ceiling_rose_looped.cs4
Notice the Blue wire coming from the switch - it has a sleeve on it to show that it's switched live and not a neutral.
You may wish to consult an electrician.
Good luck... take care...
Peccavi
June 2009