Parallel's Virtual Core and Ram assignment

Will specifying the amount of virtual core and virtual ram my vm (windows 7) will use affect the speed of my os x and its applications?

It will, if you assign all your computing power to your Virtual Machine the host system will get very slow ... in my experience I've found it's always better to limit the VM in some way

atm I have half of my CPU and RAM assigned to my virtual system ... that's 2gigs of RAM and one core ... although it might be faster not to limit cores and just assign a "slower" cpu, never got around to tryin git out since this setup suits me and runs smooth

Simply put, the more resources you allocate to a VM, the less OS X can use.

The adaptive hypervisor setting can help quite a bit if it's enabled. Basically, it focuses your systems resources on whatever window is active. Thus, if you are doing quite a bit in the Windows VM, more resources are thrown at it until you move to another application, say iPhoto. This is good if you are piddling around back an forth a lot. It's not so good if you want to run something in the background and use another window in the mean time ie: you have a big iMovie project you are importing in the Mac, and you decide to switch to Windows to use your work's Outlook email. The resources actually leave the iMovie session and go over to the Windows session, thus defeating the background iMovie process' progress. I generally run it enabled as my Windows sessions are usually less than a few minutes of using a Windows application to log my time and expenses. Don't confuse it with SUSE or AIX's hypervisors - they operate quite differently and are similar in name only.
-Dave

Thanks a lot, that was exactly what I wanted to know.