Ok, so it took me long enough to find this out. so i decided to share with you all.
Basically form the Vista Network and sharing center, you cannot disable Network Discovery or File Sharing. It tells you to do it via your firewall.
Changing the Stealth option doesn't help it.
Basically there isn't an option "Disable Network discovery and filesharing" In BitDefender Internet Security (i'm assuming its not there for Total Security either).
In order to disable filesharing and network discovery you have to open your ADVANCED SETTINGS
in advanced settings go to:
Firewall > Zones >
Select the zone (network) you want to disable file sharing and network discovery and doubleclick on it.
Change the setting Trusted/Untrusted to Untrusted.
Your network and sharing center will still say its enabled, but other computers won't be able to see you when they do a workgroup (computers near me) (NETWORK DISCOVERY IS DISABLED) and they won't be able to access file sharing on your computer by putting your computer name \\NAME in an explorer window (FILE SHARING DISABLED).
Remeber always to keep "Password Protected Sharing" Enabled.