secure networking

[Billy Joel]

Looking for information.  Does anyone know of any networking software that
can help enable secure networking.  We want to be able to define and
maintain certain levels of security on our local network while maintaining
external internet links to the rest of the world.  Is there any existing
software that guarantees any kind of security???  Can anyone point me in
the right direction to pursue this further.

Please keep your responses toward the layman.  I am somewhat ignorant
when it comes to networking.

Thanks much.
Joel Riedesel
jriedesel at den.mmc.com