<font color=blue>He just can't access the Program Files share. Is this because it is a protected or special system share? If that is the case, he shouldn't be able to access the C$ share, the system folder, etc.</font color=blue>
The default W2K NTFS permission set for c$ is Everyone/Full Control, which is why he could access the c-drive share even without credentials, I believe. Even the \WINNT folder includes Everyone in its permission set.
The default NTFS set for the Program Files folder is more restrictive, and does not include "Everyone", but only Administrators, Power Users, and Users. All of these groups require some sort of credentials to permit access.
I think the simplest way to fix it (per pbenven) would be to grant "Everyone" Full Control on the Program Files folder. This is a potential security hole if connected full time to the Internet, but a personal firewall should take care of that.