Just to throw another pepper into the gumbo, I have only Poser 6 on a W7 64-bit machine.  I installed it to the root drive, but other than that it is installed just as on my XP machines.  All of my content, including extra runtimes are under the Poser 6 folder.  I don't, however, use the word "runtime" in any but the original.  The others are named for the character, libraries under those foldes.  All geometry and texture files are in the main runtime.  I've used it several times a day for months, and have had no problems whatsoever.

I don't know about DAZ installers; I haven't bought anything from them in a couple of years.  V4 and M4 are SEP (somebody else's problem).

John