I just downloaded the FULL 2.3 SDK from your like you provided. I installed it to C:SierraHalf-LifeSDK and there is NO folder that is titiled "Source Code." There's Single-Player Source and Multiplayer Source with seperate cl_dlls folders but there is no cl_dll anywhere.
[Update] Sorry, I finally found the "cl_dll.dsp" file. Is that the same thing as the "cl_dll.dsw?" Anyway, sorry for the confusion. I'll be alright from here, thanks!