To download and install idTracker 2.1:
Download and install Matlab Compiler Runtime 8.3 (64 bits)
Download the executables of idTracker. Copy them to any location of your hard-drive, and execute idTracker.exe to start using it.
User Guide (a bit outdated, but useful)
You can also download the code (not needed to use idTracker on Windows)
You can also download idMatcher, a tool to relate the identities of individuals across different videos. To download and install idMatcher:
Download and install Matlab Compiler Runtime 8.2 (64 bits) this is a different version than the one needed for idTracker)
Download the executable of idMatcher. Uncompress it in any location of your hard-drive, and execute idMatcher.exe to start using it.
Here you can find the instructions for idMatcher, and its Matlab source code.