Welcome to the Community,
did you choose to use "Easy Install" for the installation of the XP guest? If this causes issues, create a new VM, select "I will install the operating system later" and follow the steps in http://kb.vmware.com/kb/1000863 to load the necessary Buslogic driver while installing from the Windows XP CD/ISO.
Installing "Snow Leopard" as a virtual machine may not be discussed here in the Communities, since installing it on non Apple hardware is a violation of Apple's EULA.
André