"Various tools relating to the SMI MIB Information"
If this library isn't already installed or available as a package for your platform, you can get it at: http://www.ibr.cs.tu-bs.de/projects/libsmi/.
Wireshark uses the source libSMI distribution at http://www.ibr.cs.tu-bs.de/projects/libsmi/. libSMI is compiled using MSVC++ 6.0. It's stored in the libsmi zip archive at http://anonsvn.wireshark.org/wireshark-win32-libs/trunk/packages/