I just installed the Sublime Text under Windows Vista, and even following the advice given in this post, namely to explicitly set View > Syntax > JavaScript >
Ternjs is a new alternative for getting JS autocompletion. http://ternjs.net/
Sublime Plugin
The most well-maintained Tern plugin for Sublime Text is called 'tern_for_sublime'
There is also an older plugin called 'TernJS'. It is unmaintained and contains several performance related bugs, that cause Sublime Text to crash, so avoid that.