First of all, don't worry about the college class just yet. While you may be required to have a DSLR in order to participate in the class, many colleges have a set of cameras available for students in the class to use. Mine did, and only one person in the class chose to purchase their own camera secondly. If there are cameras available, you may wish to wait to purchase one until you have a little more money to spend.
Now, moving on to the cameras themselves.
When it comes to brands, quite frankly, you probably won't notice much of a difference between the brands themselves. They all use the same basic design and principles to create images. Think of it this way: When you see a photograph in a newspaper or magazine, what does the text underneath it say? More often than not, you'll see the photographer's name...but I've rarely seen the camera brand listed. Let that be a lesson: The camera brand itself isn't important; it's who's using it and how they're using it.
But, when you stop considering the brand and start looking more at the camera models themselves, things get a little trickier. Are Canon T1Is and Nikon D5000s (I'm pretty sure you're talking about Nikon, not Nokia) decent beginner-level cameras capable of taking some fantastic photographs? You bet. But will the images themselves be much different? Nope. If you pick up a Nikon and take a shot, then you grab a Canon and take a shot...one image won't be magically better. As your skills improve, your ability to produce great images will get better, but the brand or camera itself doesn't do a thing to improve talent.
When you look at the camera specifications for the camera models you listed, you will probably see some differences. But, that chart is likely to be the ONLY place you notice those differences -- looking at the photos themselves, you won't be able to tell a difference between the 10MP camera and the 12MP camera. You won't be able to identify which one had 40 autofocus points and which had 49.
It's true that there ARE some details you might notice differences with, but they often won't create much of a difference in practical use. These two brands, in addition to others such as Pentax or Olympus, are all pretty equal in the broad spectrum of things, when it comes to the images they're able to produce.
On the other hand, even though the images themselves might not be very different, different user features are important to different photographers. Things like the weight, the grip style and material, etc., can be deciding factors in how much you enjoy your camera. For that reason, I'd recommend you go to actual stores to look at pictures. Every camera within a certain price range, such as $500-$600 for instance, will be fairly equal in specifications but fairly different in how they feel in your hands.
You say that you're considering a used or floor model rather than a new model because of price. In the end it's up to you, but I would strongly urge you to be careful if you buy a used camera. Someone on Craigslist or eBay could be selling a camera that USED to be great...but after use, it's not so great anymore. Part of the problem with that is that sellers will often say they just got a new camera and no longer need this one, or they hardly ever used this so now they're just going to sell it to a good home, etc., when in fact it has serious problems they simply don't want to disclose. If something is wrong with the camera, there's not a very good chance you'll get your money back.
I'd suggest that you save up for a new model, or at least make sure you are buying from a reputable seller. Factory refurbished models can often be good, as they have been checked out (and if necessary, restored) by the manufacturer. They often come with at least some type of warranty in case something goes wrong.
Don't forget about lenses, either. You can purchase a camera body, which means that you have to buy the lens yourself, or you can buy it with a lens. Some cameras are sold with two lenses -- usually one is a standard lens, such as 18-55mm, in addition to a larger telephoto lens that can go as high as 300mm.
Also, one other note -- looking at cameras in a store doesn't necessarily mean you have to buy it at that store. Go to a store that sells DSLRs, pick a few up, look them over, and narrow it down to a few that you really like. Then, go home for a few days and come back again, aware of which choices you liked the best. Look through everything and make sure you haven't missed anything, and then carefully go over each camera. Pick them up, look through the viewfinder, etc. Then, note the prices, go home, and look online. A while back, I was looking at a certain camera model, and figured out the lowest price it was available in town...but online, another major seller had it for a hundred dollars less.