If you don't already know, read this page to learn what a firewall really is. Lockdown resides in the Application Layer and is wholly dependent upon lower network layers. But it does not directly prevent or monitor any network traffic. For instance, Lockdown doesn't head off unwanted connections to shared resources before they happen like a firewall can easily do. It can break connections only after they are made, and because this involves inevitable delay, it may in fact do so only after files are deleted or transferred.
Lockdown does absolutely no packet filtering of any kind whatsoever.
However, it controls access indirectly, very belatedly, largely unsuccessfully and only in the very limited sphere of NetBIOS resource sharing. It operates at the application layer, far removed from the Network Layer which is the bailiwick of a packet filter. Lockdown does not validate connections or control ports used by other applications nor does it monitor their data transmissions in any way whatsoever. Lockdown2000 does monitor shared resources on the local machine but it is again dependent upon lower-level Windows processes for its control of those shares. It does not mediate the actual networking communications with those shares and cannot directly block access.