Graham - as Roz has experienced, squats and lunges are ideal. You don't have to do them with weights initially, just start with your own body weight. Vary your squat position so you hit the muscles from as many different angles as you can.
For squats start with your feet hip distance apart, with your knees and toes facing forward, squat down as if sitting on an invisible chair, do not let your knees go past your toes, stick your bum out as you go down (no lower than thighs paralell to the floor) and on the way up really squeeze your glutes. The other foot position for squats is a wider stance with the toes pointing outwards (think 10 minutes to 2 on a clock!), the rest of the exercise is exactly the same.
Lunges can be done standing and alternating legs, or however many reps on one leg then the other, or - and this is my fave - walking. Basically, take a big step forward, planting the heel down firmly and then go into a lunge trying to get a right angle at each knee and making sure that the knee of the fron foot does not go beyond the toes of that foot.
This is probably as clear as mud! But if you are a memeber of a gym, get one of the gym instructors to help you.
Good luck!
