You can't fix it yourself if the timing belt went when you were driving.
It is difficult enough to fix before it snaps (ie. before your engine has the pistons hit the valves).
I got mine changed last week for £120 as a preventative measure, but if your cam belt snaps while driving your engine will often take a lot of damage, and this is only fixable with new engine parts.
Just to change the belt (without the engine fix) involves taking the side of the engine off and messing around with the tensioners- you have to make sure the belt is on correctly otherwise your engine won't work.
Buy a Haynes manual for help, but from the sounds of things your problem isn't just the belt that needs replacing, but the engine which needs work.
Jonathan Senior, March 2005
