So I should figure out how much RAM, hd, etc. I need for "one" OS (and one AC) and double it for the computer that I need virtualization on?
I have 2 computers running AC on both the host and a guest operating systems. Both are 3 year old Dells with Intel Core 2 Duo CPUs and 4 GB RAM and 160 GB HDs. I have one with Windows 7 Pro and one with Windows XP Pro as the host OS. Both of my guest OSs are Win XP Pro, since I could use the Win XP verifications codes from old computers, and Win XP needs less RAM to run fast. I gave each OS 2 GB RAM and the guest OS has 60GB HD space.
To sum up, these machines are very easy to use and switching between the host and guest takes a mouse click. There is a very slight performance lag when running the virtual machine.