Hi Kevin!
This might not be the best forum to ask this on, but I did a little research. The fields "mathematical neuroscience", "computational neuroscience" and "neuroimaging" are very hot fields. Take a look at following links:
http://www.whydomath.org/node/HHneuro/index.html
http://neurotheory.columbia.edu/~ken/math-notes/
Apparently, in uses nonlinear dynamics a lot (which is very interesting!). In any case, you will want to do an applied mathematics program with focus on differential equations, statistics, analysis, Fourier analysis, neural networks,...
I have a bit of experience in neuro-imaging and image-compression, but it is a very interesting field. It uses quite a lot of deep and pure mathematics (mostly analysis, functional analysis, etc.). I've had the honor of following a class of one of the prominent figures of image-compression, professor Daubechies. She did a double major in mathematics and physics in my university, and worked in quantum mechanics for a while. But she then switched to image compression and did fabulous work there. So I guess that an applied math/physics degree does prepare you sufficiently for an applied carreer.
If you want to consider this path, then an applied mathematics degree is useful. Taking classes in computer science, physics and engineering is very advisable. Be sure to find a school were applied stuff is popular, though, as many pure mathematicians can get bogged down in theoretical details that don't matter...
As for job prospects and whether mathematicians really have a chance of becoming neuroscientists, you will probably have to ask people working in the field. I don't know if there are such a people on PF...