The advice you have been given to install on the ssd and disconnect all other hdd's is valid. Installing with the other hdd's connected would mean that the boot files will finish up on one of the other drives and a delay in boot time. Not what you want when spending $$$ on a ssd.
The easiest way would be to install W7 on the ssd on it's own and reconnect the drives when finished. You can then enter the bios and change the drive boot order to the original boot drive when you need the other os.
Or you can download a free bootmanager like EasyBCD.