Unlike a printer, a computer is something that you'll want for your very own (very soon). We don't suggest relying on computer labs or friends for this.
So many choices
There are a lot of choices out there, so let's keep it simple: we suggest Macs and we suggest laptops. With a well outfitted laptop, you can run the applications (CS6) easily and do what you need to do — plus it can be portable if needed.
There's nothing wrong with an iMac or MacPro, but it unnecessarily ties you to your desk and — in the case of a MacPro — is more computer than you need unless you're doing processor-intensive CAD, 3D, animation or video work. I do everything on a 13in MacBook Air.
Plus, when all of your friends have Macs (and likely the same printer), troubleshooting will be much easier.
However, we don't suggest doing actual design work on your 13in or 15in screen. Hook it to an external monitor (Apple or otherwise) and you'll have a 2-monitor set-up (Monitor and laptop screen) which is very nice.
I have found the MacBook Air to be great. The flash-drive is super-fast and the lightness of the machine makes portability easy. I don't miss the optical (CD/DVD) drive one bit — I have an external one ($80) on my desk that I've used 3 times in 3 years.
The MacBookPro is also a great choice, too... a bit more expensive and a bit more heavy. You'll likely not see the benefit in a Retina display (from a cost POV), but if price is no object then by all means, get a MacBookPro with a Retina display, 8GB of RAM and an SSD. It'll cost more than $3000, though.
When shopping, check out the "SALE" section on the Apple site (lower left column) which features refurbished and older stock machines at a 15-25% discount. I'm typing this on a refurbished MacBook Air which was indistinguishable from new.
Craigslist can also be a good way to go, however if searching for used machines, make sure the processor can run the most recent system software. Currently, Mountain Lion will not run on an Intel Core Duo (you need an Intel Core 2 Duo or newer), so a Mac older than 2007 might not work as well for you long-term — when entering the profession, you'll be expected to know the most recent software.
Also, when buying off of Craigslist or eBay, you'll want to be safe and be aware of scams or misrepresented equipment.
Make sure whatever your choice you have plenty of RAM — 4GB is the minimum. You'll notice speed boosts with more RAM over a faster processor. You'll also notice faster performance with a flash-based hard-drive (SSD). I've not used the newer "fusion" drives, but they look like they could be worthwhile.
So, from a money-best-spent POV: more RAM first > then a flash-drive/SSD > then a faster processor.
There are a good variety of accessory input devices as well. If working on a laptop, you'll definitely want a mouse, at least. I've never had a problem with wrist issues (carpal tunnel syndrome), but some folks find that a trackball or tablet (Wacom) can be more comfortable.
Also, remember to back your stuff up (fodder for another post) and use your AAU-ID to get some discounts, too — generally 10% on larger, new purchases at the Apple store.