Starting strength training - advice needed please!

Hey,

I've spent the passed 3 months mostly focusing on my cardio fitness, even though I know the benefits of weight lifting/strength training.

Today I was at the gym and wanted to start incorporating strength training into my fitness regimen, but I'm at a loss of what to do or where to start (and don't have the cash for a trainer!)

Background information - I'm looking to lose weight and generally tone up (not build crazzy amounts of muscle). My goal weight is 57 lb away.

So here are my questions...

Should I be focusing on different muscle groups each time I work out, or is it okay to do 1-2 exercises for each?

Are the machines at the gym really worth it, or am I better to be using free weight/body weight exercises?

How many reps/sets are appropriate? I've always done 3 sets of 12 reps. Some examples of the weight I used today are 45 lb for hamstrings, quads (both on machines), 70lb for the leg press, 40 lb for chest press.

I don't know whether I should focus on machines at the gym, free weights/body weight exercises, join a group class (like BodyPump at Goodlife), use a DVD like Jillian Michaels...just feeling very overwhelmed and would love to know what others have done and recomend.

Like I said at this point the goal of my strength training is to generally tone up and add some muscle to make my weight loss more effective, not looking to pack on a whole lot of muscle mass.

If you have any good websites or resources feel free to direct me there, and thanks in advance for any help you can give!