There is easy way to create the additional user on VMware ESXi 4.1 host. This steps also can be apply on ESX 4.0 or ESXi 4.0 or ESX 4.1 host.
1. Connect via vSphere client to your ESXi 4.1 server
2. On Local user & Group, Add user
3. Assign to the group.
4. Then go to permission tab
5. To assign a permission to an individual or group of users, add their name to the users and group listed.
6. Add the target user to the role you desire.