I would wait until you get there before deciding on your purchase. I've worked at (and went to school) at a few different institutions that have had varying views on student-run WiFi networks:
Some schools flat out don't allow it and actively look for wireless routers/access points via their MAC addresses/usage (not sure how many resources are used, but it's kinda like the phone tethering discussions).
Others require you to log in with any device on the network, usually through a web browser. This then records your MAC address with their network equipment and gives your computer the "okay" to use the network. This is often mixed with letting video game console MAC addresses pass through.
Some use the second method and flat out ban known MAC addresses for router brands, too. If you use an AirPort, it may be seen as an Apple computer (which can't log in), or will just not work. Routers like those from Netgear and Cisco/Linksys can "spoof" their MAC address, so they appear like your computer to the outside world. I know of a lot of people who have used this method. Unfortunately, it's not part of the official WiFi spec, so Apple doesn't include this feature.
Finally, it may just be not allowed, and you could get yelled at for using it (many lenient schools) or have your internet jack shut off (tougher ones). Furthermore, running any sort of router (wired or wireless) improperly could start sending IP addresses back into the networkwe had this bring down a wing in a residence hall once.
WiFi is convenient and great, but I'd do my research on-site first. If you can use one with no issues, the AirPort Express (any generation) is a fine product and will offer enough coverage for your room. If you can't use one, but won't get into much trouble if caught, I'd say pick up a cheapie Netgear model from Walmart or Target and have it set to look like your computer.