It would probably be best to install PC-BSD on the second hard drive as first in the boot sequence of BIOS, in case the installer doesn't have the option of not installing its bootloader to the MBR (which would end up rendering your W7 and XP unbootable), which it probably doesn't. Though I have never installed FreeBSD before, I have installed PC-BSD, and understand that they are similiar as far as underlying architecture is concerned (and I think PC-BSD is actually based on FreeBSD, so its probably like an updated version of it). Note on my system I installed it on an external hard drive, so my main hard drive's MBR was not touched at all by the installer (though that was a while back, and I only booted the OS a couple times, so I don't remember much about it). I also was not using the MS boot manager to chainload its bootloader, but was using a 3rd party boot manager instead. Due to this fact, I have not tested booting it with the help of EasyBCD adding an entry for it to the boot menu. I would assume it would detect it on another hard drive just fine, but its probably best to create the entry after the OS is installed (not before), since I don't know how the internals work.
Btw, now that you reminded me of PC-BSD, I'm considering hooking my computer up to my external hard drive right now, and see if I can load it through my W7 boot manager (after first adding an entry for it in EasyBCD, of course). I'll let you know how it goes.