I found this to be a problem myself, as anyone with admin privs can access your hd over the network. I found the solution in a Tech Republic article a couple of weeks ago. You need to open regedit to create these keys as follows. One thing that found to be untrue is the note about win2k. This didn't work, until I added both keys to the registry. Be very careful about working in the registry, as mistake can have very frustrating effects on your day to say the least.
Create values for AutoShareServer and AutoShareWks:
In the registry, locate the following key:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\LanmanServer\Parameters
On the Edit menu, click Add Value .
Type AutoShareServer , click REG_DWORD , and then click OK .
Type 0 , and then click OK .
On the Edit menu, click Add Value .
Type AutoShareWks , click REG_DWORD , and then click OK .
Type 0 , and then click OK .
Note: Sometimes the values are already present, especially after use of a policy that affects these entries. In addition, on Windows 2000 you are not required to add the AutoShareWks value.
Quit the registry, and then restart the computer.
Enjoy!