The coretemp-isa-000X sensors sense the temperatures of the cores of intel dual core CPUs (1 for each core). I think acpitz-virtual-0 is the sensor of your laptop's motherboard, probably northbridge (with the graphics core in it), southbridge and a external CPU sensor.
If you can see the temperatures in the BIOS (my laptop BIOS doesn't show them, but my desktop BIOS does) you can compare the values there with the values you get from lm-sensors. If you let your laptop run idle for a few min and then reboot into the BIOS the temperatures will be more or less the same.
You can also stress different parts and see which temperature increases. For example glxgears (terminal) will stress your CPU and graphics core. And you might be able to tell which temperature is the southbridge by stressing your network (is likely connected to your southbridge) or copying files on your disk.
Well I figured it out....temp1 is GPU, temp2 is the Southbridge and temp3 the Northbridge...thanks!!!