The company needs to be proactive about this.
- Check the license. Some software licenses allow businesses to give employees a copy to run at home.
- Run license servers. Try to purchase software that requires a running license server at the office - the software won't run without it.
- Use dongled software. The software is then attached to the dongle. The user can use it at home, work, the pool, and they can't (easily) break the license.
- Log all installs. Lock down the network drive, have users send a request to have it unlocked for them for a period of time, log accesses so you know which software they installed/copied and keep the records. Make sure they know you do this, and even though you can't tell whether they took it home on a flash drive, the fact that you are watching and there's a process will deter most people.
- Limit software installs on the network drive to those that have licenses you can protect (license server, dongle, or software that users are allowed to take home, for instance) - software that doesn't meet the requirements has to be installed by IT.
- Use software on the work PC that can determine what is installed, and log network accesses to the software install drive. Occasionally compare what has been installed with what is accessed - when they've accessed something that was already installed or something that was never installed send an automated email requesting an explanation. Perhaps you'll never act on it, but the fact that you are actively monitoring this will deter most casual users.
In general, if you leave the candy store open and unguarded you will necessarily allow some people to take and use the candy for purposes you don't allow. At the end of the day it's a choice between making things easier or more secure, and the balance is always difficult.
Many companies lock it down except in cases where the user has a valid reason to install software on a regular basis. Except for software developers, IT professionals, and similar employees, the vast majority of computer users never need to install software themselves.
In the case of those that do, they generally can get around whatever you might put in place if they want to.
So, most companies take a hands-off approach.
Keep in mind that if you only enforce it using written policies and procedures, but put in no technical protections, you may be safer than if you put in some technical protections. The employee is always at fault if piracy is found, but if you make a half-hearted effort then it may be argued that you are liable, but didn't do enough. This could be especially damaging if one of your employees decides to torrent your software and licenses.