1) How much water are you drinking? I always recomend more water to those people who complain of joint pain/popping. I did this myself and my painful knees, popping jaw and stiff back all but disapeared. This also includes not consuming ungodly amounts of caffiene and alcohol a day, as these both are diurretics and pull water out of your system. A coke or a cup of coffee is about the max caffiene you should be taking in...But anyway, drink more water! I shoot for 10-12 glasses a day.
2) You have to make a real effort to correct your posture. Without knowing what kind of posture you have, I cannot really make any 100% accurate reccomendations, but there are a few basics you should always do. Stretch your hamstrings! Tight hamstrings cause your lower back to pull in, and since you sit alot I bet yours are quite tight. Workout that back! Good Mornings, lat pulldown, seated row, bent over row, shrugs, rear delt butterflys... Match those exercises up with plenty of Ab exercises. The main cause of bad posture is muscle imbalance. If you sit tilted forward and slumped alot, your chest will be caving in and your shoulders will be streching out. Chest exercises must be balanced with upper back and shoulder exercises, and visa versa. Most of all, KEEP STRAIGHT!!!!!! Strenthing and balancing your muscles will help, but without a conscious effort on your part, your posture will never improve.
3) Cardio man. Get on a treadmill, eliptical trainer, stair stepper, even a stationary bike for at least 20 minutes 3 times a week. Keep your heart rate up, burn some calories. Strengthen your legs up as well. Squat till you drop! Sqats are the most perfect form of leg exercise, since all the muscles are used during the motion. Other good ones are calf raises, leg press and lunges.
Most of all, go to your local gym and make a few appointments with a local personal trainer. I can only help so much without phsically seeing you and testing your strengths and weaknesses.
Hope that helps some
