Ah, what a great time .. college life in Uni..

Most colleges will have rules about people not using wifi routers as it will clog up the limited amount of bandwidth on 2.4ghz and cause issues. It is also not easy to fit a TC into a non-apple network. And depends very much on what kind of logon is used.. many systems use some kind of html login page.. designed to kill off using wireless routers. If it uses a standard wpa or wpa2 password you may be able to use the TC as a wireless client, but then this can lead to issues as you with either need a second IP if they run the uni system properly it should not do. Or you will have to NAT the IP.. and that can lead to issues if you already get a private IP.

The trouble with just using the TC as a wireless backup without putting it into the network is that wireless client cannot connect to two different SSIDs at the same time. So if you use the TC off the network.. you will need to use the laptop off the network whilst it is doing backup.

It is possible to use a second usb wireless client in the lappy.. just need to find one that is Mac compatible. These can be pretty tiny and only cost a few dollars. It would also be great to use 5ghz but they tend to be more expensive and harder to get.

Also I do not know how to turn off wireless on 2.4ghz in the standard dual band TC.. ie just run it at 5ghz. It may not be possible. The older Gen1 TC which is not dual band can be set to either 2.4ghz or 5ghz.. which in this case would be great.
Security is fine.. just set wpa2 and use a decent password.. TC is not vulnerable to the new WPS attack.

Sorry my answer is getting messy..
I suggest you play this by ear.
You can use the TC just by ethernet.. with wireless turned off.. and this is the easiest way. But you do have to plug it in. And an external hard disk will do the same thing. Without being any more hassle.
You can also do it by using a second wireless like USB. And that can work easily and effectively.. without too much intrusion.. or extrusion.
But getting the TC to exist inside a network that the uni provides is likely going to be a big pain.

You could also disable wireless on the TimeCapsule completely and just plug into one of the ethernet ports when you want to backup...making it pretty much an external hard drive. That's probably the most secure way to do it.

Originally Posted by The_Hawk

Like get a Mac mini, connect it to the WiFi network and use it as a HTPC which is left permanently on, then add a USB WiFi dongle to the Mini and share the Uni's internet connection through that to your MBA.

Remember he/she is a student, which means he/she is probably living on a students budget, which means thats probably a no go (although it would be my first choice) Been a long while since I've dealt with a time capsule, but if your room has ethernet you could plug that into the wan port on the capsule, then crank the wifi strength way down so it only creates a network big enough for your room. Just make sure to setup secure passwords. That way all your problems are solved.

I still suggest you check the rules.. and login methods.. merely having ethernet does not mean you can actually connect if it uses a html login page. Nor does it mean you can run your own wireless.. If you run wireless via the uni and ethernet as well, and try to backup over the network, I doubt the security of the system will allow that to happen either.
Imagine if you please, 50 or 100 students in rooms.. everyone with their own wifi router.. the result will be unworkable.