According to PC World it should download and install automatically the next time you start Chrome. Worked for me but did take a while.
Update: Well this is great! Windows Secrets seems to be working much better in Chrome 9 than it did in FF 3.6.13. Looks like I'll be using Chrome at least for my WS work! Everything is quicker and works better. I even installed the Script to highlight forums with unread messages in Yellow, works great. You do not need to install GreaseMonkey the scripts are supported natively in Chrome 9! Just drag the file into the Chrome window and answer the install prompts & restart.