It just says one graph per cpu, there is no other option.
also did some digging around and found a post xp sp2 hotfix for dual core cpu's and performance problems. Which did seem to improve performance, but it still shows as one CPU, looked in BIOS nothing in there to enable.
Are we certian a Dual core cpu should show as two CPU's under Taskmanager. seen this post but its refering to AMD cpus