I've got a MacBook Pro, and it's served me fine for whatever Maths I've needed to do (with Maple, Mathematica, MatLab, R, and graphing using Grapher!), but I don't take it to lectures - absolute nightmare to try and keep up with my lecturers without having to learn how to enter TeX into. You can run Windows, as people have clarified, on a Mac, either with BootCamp (advisable), or Parallels (less advisable!). But I was fine on my old PC for a term (before it gave into old age), so you'll survive either way!
Hope that helps,
HenryT