Hello,
The easiest way is to check in your system menu, on system information
Then click on the more detailed button
and if you see there it shows information for
CPU 0
and
CPU 1
Linux IS using your two cpu's,
also, if you want to keep track of their usage, you can download a very nice monitor that will let you see the activity of your cpu's, hardrive, disk drives, memory, etc...
Gkrellm
http://web.wt.net/~billw/gkrellm/gkrellm.html
check it out and try it, you'll like it,
zLinuxz