I was going to write an article on this, but it was so easy, there is no need for one.
Windows 7 doesn’t know how to deal with PC-BSD, but PC-BSD knows how to deal with Windows 7.
So all I had to do was install Windows 7 first (I chose a 50 GB partition) and then I installed PC-BSD on the remaining space. I did click to install the PC-BSD boot manager as it is not selected by default, and now I can dual boot Windows 7 and PC-BSD. Which is a must for a guy who’s job is writing C# on windows.