You can get the current version of the DLL SDK (version 2) from here:
http://www.outpostuniverse.net/files/coding/op2_dllsdk.zipI'll explain the layout of files within the ZIP:
Lib\ -- contains the library files you need to link to Outpost2.exe.
Multiplayer Hooville\ -- a working LoS multiplayer map, made by Hooman. (there is a lot of useful code in here! But *please* don't pass this off as your own work).
Outpost2DLL.h -- OP2 header file. Should be pretty apparent what this is for :-)
As requested, I'll close this topic.
Edit: Updated link.