Is the cores can be splitted

Hi Team,

I have a Single Quad Core processor with 2.33 ghz and 20 GB RAM

How many VMs can be insalled example OS  windows server 2003 and exchange server sql server

Is their an option to split my available cores for example i have 4 cores can i split it into 1,0.5,1, 0.5 and 1

So that i can have 5 VMs in my VMbox

How to implement networking in vmware

is must to have vlan and vswitch in the network

suggestion required

thanks