JAMDR-
I had a Mac-PC experience during my EE Masters... I switched to a PowerMac midstream... started on a Win2K PC and finished on a PowerMac G4 (2x 1GHz) . I completed my academic work and all my publications strictly using the Mac w/ my existing PC software using VPC6 (MatLab, MathCAD, and MS Office since I already owned them) and wrote all my reports and final thesis using TexShop, Gimp, & Graphics Converter. A complete PC to Mac academic transition in ~ 1 months time having never previously used a Mac ... sounds like a commercial, eh?
That being said, my department did not insist that any particular software tool be used for anything. If your department insists on seeing a nice MathCAD printout when you turn in assignments it may, IMHO, be frustrating to run on with VPC which will probably be sluggish and have slower computational times (app is 10:1 slower versus my AMD 2200 XP PC). On a Mac, I would opt for using MatLab or Mathematica if possible since they are both better tools anyway and I seem them used professionally all the time.
So, there are two schools of thought here...
... as an engineer in the real world you will have a variety of problems in front of you and you'll not always have the perfect tools to use or you'll have to use/learn some other tool that is available. That school says "hey, go buy a Mac and figure it out later" ...
... On the other hand, there is something to be said for making school as easy as possible so you can focus on accomplishing assignments, learning the material and leaving enough time to go drinking. Throwing another obstacle in your way may take away from your learning/social experience. That school of though may say buy a PC laptop.
My recommendation ...
Consider the availability of PC computer labs at your school and whether your current PC is "good enough**" to bail you out if you need it for some nitch software package. If this is the case, buy a PowerBook and be happy.
** What field are you studying and what are the specs of your existing PC? Most engineering students think they need more computing power than they actually do ... I finished my BSEE using a PI, 90 MHz using MatLab and PSpice heavily.