I dont think waiting for a Intel Mac is a good idea. Especially since we don't have any clue what will happen when you try to dual boot. For one thing Apple is obviously not going to make drivers for their systems to boot on Windows. You might find yourself booting up windows but not able to do anything on it.
As a computer major I really do not think you need a super beefy system. You can probably get some cheap used old system for 200 bucks that might be 1 year old. Might not be top of the line, if ever, but as long as it runs the applications you will need in the future it will be great.
By now havent you already registered for your classes though? I know as a Freshman myself entering in college I registered for my classes 2 months ago and already know what professors I will have and all that jazz. You should definately try contacting those professors and asking them what they perfer.
As a switcher myself though Ill be bringing my 12'' PB and my Shuttle system. I have yet to know what to expect for myself, but atleast I'll be prepared on both fronts.
My best advise to you right now is to wait it out right now. Hold off on the iMac and see if you will need a PC system. If you don't, do whatever you want and get your iMac
OR you can skip out on the 20'' iMac, get the cheaper version of the 17'' iMac, take the money you saved and get a really cheap dell system. Ive seen lately some dell laptops sell for about 400 bucks and full systems (monitor, mouse, keyboard, etc) sell for 600. So just play with the numbers if you absolutely want/need both.