well if you have XP (home or pro) or 2000. You CTRL+ALT+DEL
You should see 2 line graphs for each cpu (1 physical 1 logical)
But make sure you hit VIEW> CPU History> and check ONE GRAPH PER CPU
If you think you have HT, but it is not enabled..... Go look for the hyperthreading settings in the BIOS and enable it if possible. If it is grayed out, your cpu is most likely not compatible.
You will 2 graphs right next to each other in the CPU usage column if you have HT (like the pic below)