You have probably come to this page from an old link. Click here to go to the new download page for TCD Simulator Version 3.2 (recommended).
The old Version 2.3 is still available for download (see below). In addition to newer Windows versions (7, 8 and 10), it will also run on Windows XP and Vista.
Download the setup file Setup-2.3.exe (about 4 MBytes)
After the Setup-2.3 program has been downloaded, just double-click on it to start installation. In Windows Vista, you must be logged on with Administrator privileges to install the program.