New CPU, enable SMP

Hi all,
I just replaced my AMD Athlon64 3500+ (single core) with a dual-core 4200+. Do I have to do anything to get FreeBSD to access the extra core? I made sure options SMP is enabled in the kernel config.

Is there a way to dynamically check to see how many cores it recognizes?
And also top -P should show how many CPUs are used (and how).
$ sysctl hw.ncpu
hw.ncpu: 1

$ dmesg | grep -i cpu
CPU: AMD Athlon(tm) 64 Processor 4200+ (2200.10-MHz K8-class CPU)
cpu0: <ACPI CPU> on acpi0
powernow0: <Cool`n'Quiet K8> on cpu0
acpi_throttle0: <ACPI CPU Throttling> on cpu0
What gives?
Maybe the second core is deactivated in the BIOS. In FreeBSD 7.1 the default kernel is an SMP kernel, so you do not have to activate anything.
I have read somewhere online that some motherboards require you to flash the BIOS when replacing a CPU (especially if you are adding cores)... could this be it?

I'll double-check the BIOS.
It might be that the CPU was not available when your motherboard was built and you require a new BIOS version.
I'd like to attempt a custom kernel on my X2 - currently ;

$ cat /var/run/dmesg.boot | grep CPU
CPU: AMD Athlon(tm) 64 X2 Dual Core Processor 5200+ (2700.27-MHz 686-class CPU)
FreeBSD/SMP: Multiprocessor System Detected: 2 CPUs
cpu0: <ACPI CPU> on acpi0
cpu1: <ACPI CPU> on acpi0
SMP: AP CPU #1 Launched!


$ top -P [sniped]
CPU 0:  0.0% user,  0.0% nice,  0.0% system,  0.0% interrupt,  100% idle
CPU 1:  0.4% user,  0.0% nice,  0.0% system,  0.0% interrupt, 99.6% idle

Is CPU0 even used? And is all that is required is to leave in my KERNCONF;

options 	SMP			# Symmetric MultiProcessor Kernel
device		apic			# I/O APIC