A bit of a cheeky response, but get a Mac
I can run all the OSes using virtualization on one machine all at the same time. I can xfr files between them, cut/paste between them etc. However, I'd suggest using a source code version control system (like SVN, GIT, etc) for the sharing of files between projects. Also, I don't see any noticable difference in performance between my virtualized Windows and that of a Wintel box -- even for compile times.
OK, so the non-cheeky answer is to look into using virtualization in general, doesn't have to be on a Mac of course.