I would agree with David and start with a featherweight (12kg).

Download the rules from the FRA homepage and have a read through them. Anything you are unsure about, just ask on here.

Do you have any ideas of what kind of a machine you would like to build? I suggest building something more than a simple rammer as it makes it more exciting.

A few sources for parts,

http://www.technobots.co.ukwww.technobots.co.uk
http://www.gimsonrobotics.com/www.gimsonrobotics.com/
http://www.robochallenge.co.uk/www.robochallenge.co.uk/
http://www.robotmarketplace.comwww.robotmarketplace.com

The last site is based in the states but has a number of more exotic parts