4 GB RAM is the recommended minimum for your Mac to have if you want to run Parallels on it. 32 bit Windows 7 or 8 needs a minimum of 1 GB RAM to run smoothly, and the 64 bit versions require 2 GB RAM. OS X itself only works well only with 2 GB RAM minimum. So with 3 GB RAM you are running pretty much on the limits of these OSs for 32 bit Windows, and if you are using the 64 bits versions then forget it.
Note: you don't have OS X 10.7.8, most likely you mean 10.6.8.
Consider upgrading your RAM it will boost the overall performance greatly.
Last edited by a moderator: Dec 3, 2012