It'll depend on Win XP x86 vs x64. You can find some details on memory and CPU here - http://support.microsoft.com/kb/888732. With XP x86 that is two CPU slots so you could throw 4 vCPUs at the VM if you configured the CPUs with either 4 cores and 1 CPU slot or 4 cores and 1 CPU slots.
I believe XP only supports up to 2TB per drive as it does not support GPT. Are you looking to limit the disk space used by a VM?