How to determine if Hypter threading is enabled

How does one conclusively determine that hyperthreading is enabled and running?

I'm running the current generic-pae kernel with SMP support (for ubuntu 10.04), but looking at /proc/cpuinfo reveals that there are only two cpus on my core 2 duo - I would have expected 4 for HT? However if I look at dmesg I see that it reports there are two cpus and two hot plug cpus - it says that it only brings up two CPUs though. When I add acpismp=force and ht=on to the kernel boot parameters I see no change to this information. Is this right or am I missing something?