I came across these links:
http://source.valvesoftware.com/sourcesdk.php
as well as
http://halflife2.filefront.com/file/Compiling_The_HalfLife_2_Source_Code_Video_Tutorial;60668
Based on what I can tell from previous posts people have made, being able to truly re-do or remake VtMB/TFN would require the source code engine used for HL2. Valve provides that free to people on steam who've purchased one of their games that use that engine, for the purpose of making mods for those games. Can the stuff provided by Valve actually serve our purposes in terms of re-working VtMB? I have no programming experience so I cannot tell if this info would be useful or not, so I need people's input on that.