I have just installed M3 base, all his updates, and morph packages on a W7 PC 64 bit.  It went smoothly without any errors or post-installation problems.  And M3's head morph is the old installer.  I agree with Laurie, there is something unusual with your PC or file arrangement.  At this point, more details are needed to isolate the problem, maybe screencaps of your installation workflow could reveal the nature of your issues.