XP File Sharing Question, Local Computer Users Only

I am setting up our PC in my small business.

One Administrator account and several Limited User accounts planned.

I do not want Limited User accounts to access the any hard drive files accept

programs and their own data.

Currently, any Limited User can just go to the C: drive (hard drive) and

open and access any folder and file, even windows directory, et cetera. Not

good.

Please help.

Jim