This might not be a satisfying anwser for you but here are my 0.02$:

Win95, 98, Me, have no security builtin at all. It's VERY hard (I'd personnaly say impossible) to keep users from messing with the system. I haven't tried such security programs but I've heard good about Deepfreeze (which ensures the system always boots like new but doesn't prevent users from doing stuff ). The thing is, most security programs for win9X, can be screwed with through the registry (MS's poledit (security policies) for example are only registry keys that tell windows what to allow) but anyone can pretty easily modify the registry.

The ideal solution is to run NT4 or W2K with NTFS partitions and proper permissions set. NT4 and W2k can also have permissions set on registry keys (regedt32.exe). W2K with Active Directory is also quite cool with the group policies which allow you to manage a whole domain at the domain controler...

Ammo