I own the "Extreme" version of this, so I don't know if they have the same build quality, but I can vouch for the durability of the Extreme version. I am no lightweight and I started using it when I weighed about 253 lbs. (I am 72 inches tall FYI). I couldn't do a single chin-up (and obviously I couldn't go a pull-up), so I just tried my best to dead hang. I bought a resistance band (the ones that look like a huge rubber band), tied it around the bar, and did band-assisted chinups. I went from 1 band assisted chin-up to 3 unassisted chin-ups over a few weeks. Sure, it was slow progress, but it was progress. I didn't think my door frame would hold, but it does fall within the specifications that the manufacturer suggests, and it does hold my big butt up! I keep it up all the time, and usually when I walk by the door, I'll do a couple of chin-ups. Bottom line: if your door can handle your weight, the bar will handle your weight. You might not be able to do one chin-up or pull-up initially, but practice and you will crank them out in no time!
P.S. I was like 277 lbs. at my heaviest, and I'm down to around 243 now. Everyone wants to do P90X, and so do I eventually, but I watched those videos, and if you never exercised hard before, you will have problems, because it's just high intensity interval training for a long time. Personally, I would start with something called the "Spartacus Workout". There's a free guide on the Men's Health website, and its a full body workout that uses very low weights. Try that as a base, then jump to P90X. Good luck everyone!