I bought 20 PC's for the company. I know have to install several programs such as office, networks, emails, other company programs etc. is there a way to copy the hard drive from one computer to another or do i have to do every computer seperately?
It is called disk cloning and you can do it with no problem if the computers are identical.
Unless you are prepared to cough up the cash for a commercial solution you will want to look at free programs called g4u and udpcast.
You can also use the HDD manufacturers utilities to do this as well...their utilities have come a long way and actually work rather well.
Another fine program for this would be Acronis' True Image...