I want to tone my bum and thighs!

Zumba.

Walking lunges and squats.

For a walking lunge: take a long step forward, far enough that you will be going down into a lunge. Watch your knee, make sure it doesn't go in front of your toes. Go down as deep as you can without letting your back knee touch. When coming up, you'll be pulling forward onto your front leg. Pull your back leg up so your foot is by your knee and you're balancing on the front leg, hold for a few seconds. Then step forward with the leg that was in the back. (This is why it's called walking.) Go slowly, paying attention to form. You want to be pushing up through your front heel when you come up, so you feel it in your hamstrings and glutes. This is also good for your core, as you are balancing as you come up (don't worry about wobbles or even putting your foot down, just move back into position and keep going). Ten steps down and ten steps back is one set (so it ends up being 20 total, or ten on each leg).

For squats, get one of the large exercise balls (start with 65 cm, I think). Set it against the wall so it will fit into the curve of your lower back. Take a step outwards so you are depending slightly on the ball to not fall on your tush. Slowly lower down (the ball kind of rolls up your back) until you are in a sitting position, hold, the slowly go back up. Again, watch your knees, they shouldn't go in front of your toes (this is on benefit of using the ball), and make sure you are pushing through your heels so you feel it in the glutes and hamstrings. Take 3 seconds going down, hold for 3 seconds, take 3 seconds going back up, then start back down right away. 10-12 is a good starting set.

I never waste time on the silly machines in the gym. These two exercises work every muscle in the thighs, hips, and butt, and it's much less time than working each group alone. If you feel like your inner thigh needs a bit more, you can turn your feet out slightly on the ball squats (turn from the hips, not the knees), but otherwise, feet should always be pointing straight forward, especially on the lunges.

tricep dips? xxxx

In addition to the toning excercises above, the bike is great too. It really helps to tone knees and burn any fat off. Make sure you break a sweat. Its not about going so hard that you have to stand up to push the pedals. Do make yourself work for it though! Its easy to have a relaxing bike ride at the gym... but keep in mind its a workout