Heard good things about p90x. Also, if you're looking to build muscle cardio is not the way to go. Unless its low intensity.
Can still build muscle and do cardio, not combined but certainly in the shape of a circuit. If you're getting started I'd recommend going to a gym so you can see other people workout and see their form, especially on exercises like deadlifts, squats and cleans. Start off by having a plan, rather than turning up to the gym and using every machine there. Say, monday back, tuesday shoulders, wednesday chest, thursday arms, friday core & legs, doing some cardio as a warmup and cooldown. The most common fail I see at work is inexperienced people attempting to do a full body workout on every machine not only using bad form but also using machines that hardly work the target part, like the abs machine, god I hate that thing...Only old people, beginners and teenagers use it.
Start off light focusing on good posture and form and increase the weight from there on. If you want to build strength load up the bar/dumbell with enough weight to just about do 4-6 reps. If you're looking for size then load it up with enough weight to do 6-10 reps and if you want definition use a lower weight and do 12-16 reps. Train a specific body part per session, don't suddenly go from doing some bent over back row to doing legs for example, focus on working all the muscles on that session, so if it's back do shoulder press/shrugs for the top, bent over row/lat raises/front raises/flys for the middle and deadlift for the lower back.
Cardio wise do interval training. So if you're on the treadmill for example, start off with a warmup obviously, slow walk into a gentle jog, then do 1 minute sprint ~17kph and back down to 13kph to recover for another minute, then back on the sprint for another minute and so on. That'll get your endurance to a semi decent level in no time. Don't bother with cross trainer, I find that useless and effortless, it's mainly momentum in my opinion. Stick to treadmill, bike, rower and swimming. Swimming will be great as you have to learn to control the breathing, so it'll help you more than the others, and with the swim you're also working the entire body. Legs, core and upper body. Do for example 1 length sprint front crawl and use the length back to recover, either a slower front crawl or breast stroke, preferably slow front crawl, breast stroke is for for weak regulars.
