Hey there are a few different bars out there you can buy which use different methods to hold themselves up without mounting in the doorway. Just search around. I've heard some good things about this one in particular though: http://www.easychinupbar.com/homepage.asp
Until you get something, you can hang from the door itself, if the hinges are up to it. If you are afraid you will damage them, wedge something under the outer corner between the floor and the door. Get a pair of work gloves or throw a towel on top to protect your hands. Wear long pants so you will slide easily up the door.
It is a total bitch to put together. You need to use two wrenches at once to bolt the parts together, as the nuts seem to the the type that lock tight to the bolts as soon as you start turning. Worse yet, on two places where you have to bolt the pieces together, you have to do that setting of the bolt/nut INSIDE the bar, which you take an end cap off of so you can work inside it. So you have very little leverage. And you need a small wrench to fit in there that I'd guess most people would have to go out and buy especially to put this thing together, as you can just use an ordinary size adjustable wrench. This is for the wrenchaholic.
The nuts are so ridiculously hard to screw through the bolts that I think it's worth going to the hardware store to get different bolts. I've assembled a fair number of things and have never seen bolts that seem to lock like this as soon as you get them screwed down an 1/8 of an inch on a very long bolt.
That's another thing. The bolts are very long and will stick out a lot when I can actally find a way to get them fastened. I'm not a big fan of extra things to poke or scrape yourself with, but so be it. Just poor attention to design detail.
Finally, the lat bar is cool enough and the entire unit is made out of sturdy metal you wouldn't hesitate to support yourself on it(except for perhaps the most important part, the part that supports the unit on the door). But it's unfortunately held in with screw pressure on the surface of the metal, not by being bolted in securely. Simply drilling a hole in the bar would have made a lot more sense. As it is, you have a nicely enameled surface that immediately must be scraped away to assemble the unit, juch less use it and subject it to stress. So much for the enamel.
This thing is just full of oversights and sloppiness. Maybe the made in China has something to do with it, I don't know. Safe to say I wouldn't have bought it if I had known then what I know now about the extremely user-unfriendly nature of the assembly of this thing.
I have no idea how you could have said there is nothing to screw in. Maybe you meant after assembly, because there's plenty to screw in and it's very badly arranged.
In my dorm room, there were two dressers about 7 feet high so I, well actually my dad, bought a length of bar from the hardware store, got to blocks of wood, drilled holes into them, and stuck them on the ends of the bars. That way I could put one block on each dresser and the bar wouldn't roll. Total cost wasn't much and it would hold over 250 pounds.