As a huge fan of Logic Studio, I highly recommend a Mac if you can justify spending a few hundred dollars for the premium. I Have a Macbook Pro Laptop, an Apogee Duet Preamp Interface, and Logic Studio, and I find that the sound is really top notch. Macbook was like $1100, Duet was about $500, and then microphones. The great thing is that it really is plug and play. I never have to mess around with error messages and other hassles like that.
That being said, if you want to go the protools route, you can build a kick-ass system for like $600 bucks and then spend the dinero on MAudio/PRotools.
Logic and Apogee only run on Macs.
Hope this helps