I haven't had any problems getting Ubuntu to dual boot on a PC following
these instructions. You can also still buy some Windows laptops with Windows 7 installed.
I'm personally a Mac person and I run quite a few analyses in AFNI and Freesurfer on my Macbook Air (which is now 2 years old). You can run AFNI on somewhat modest (by today's standards) processors, so any of the Mac laptops will work fine. The biggest performance gains are likely RAM (4GB minimum) and SSD hard drive (Solid-State Drive).
