Need PC Lockup tools

Hi

I have some very unfriendly users that make my working environment hazardous by deleting my operating system and program files, installing unwanted programs etcetera.

I need to lock my pc’s effectively and are looking for a suitable program.

The operating systems varies from Win95 to WinXP. The usual programs are installed.
Some of the computers do lock-in to a domain.

Ps. I live in South-Africa so the tool need to be cost effective because of the currency exchange rate

Thanks a Mill

Melt