I agree with whoever said you need to focus on portion sizes rather than dieting. Also, be careful with low GI/high fat foods, cos there are plenty of them around! Remember calcium is important for muscle function, so protein-rich foods containing calcium will help satisfy your appetite. Milk is good for after exercise.
Also, when using weights, you need to increase the weight you are lifting regularly otherwise your body quickly gets used to it and you don't challenge your muscles anymore. To increase strength (and so increase your metabolic rate and calorie-burning potential) you need to do fewer repetitions of heavier weights - so don't do 20 reps of a fairly easy weight, do 10 reps of a weight that you can barely lift by rep 10. Agree that free weights are much more challenging and give a much better full-body workout.
Also, remember that your body needs 48 hrs or so to repair the damage and thus build strength after a weights session - so you should only do resistance training every other day at most. For a beginner/intermediate 3 resistance sessions a week should be plenty.
You need to vary your CV programme as well - again, your body learns quite quickly to cope with the work, so in order to challenge it, you need to try different things (eg cycle, treadmill), increase intensity so work really hard, also as someone else said interval work is fantastic.
You can also do intervals of cardio work and resistance (weights) - 5/10 mins high intensity cardio, then 2 or 3 sets of a multi-joint exercise like squats or lunges.
Breaking exercise into chunks rather than doing it all at once (ie 2 20 mins sessions daily rather than 1 gym session) is more beneficial. For example, if you took up running you could do a quick jog in the morning or at lunch time, then nip to the gym for 20 mins cardio plus some weights in the evening.
Phew! Good luck with all that - and let us know how you get on