Security issues/software

Looking for software to run on W2000 based workstations, with W2000 Server. Software needs to "spy" on employees. Security issues are at stake and my client needs a good software to see the where and when of what employees are doing on company computers.

Any advice would be greatly appreciated. Not looking for free or shareware necessarily, just something that works exceptionally well without the staff being aware that it is being done.

I have done some research, but there is so much out there, I really would like some other opinions. Thanks.