Windows only: The latest beta version of Google Chrome adds support for user scripts, but if you want to enable them you'll need to follow a couple of quick steps.
The first step is to download and run the Google Chrome Channel Changer tool, which will subscribe you to updates from either the Beta or Dev channels—you get more features but potentially a less stable browser. For user scripts just choose the Beta channel, go to Help -> About and click the Upgrade button, and you'll get the latest beta version.
Next you'll want to open up your favourite file manager and browse down to the following path for your Windows version:
Windows XP: %userprofile%\Local Settings\Application Data\Google\Chrome\User Data\Default
Windows Vista: %userprofile%\AppData\Local\Google\Chrome\User Data\Default
Create a new directory called "User Scripts" inside the Default folder. This is where you will need to save the Greasemonkey scripts.
The last step is to modify the Google Chrome shortcut—or any Chrome "application" shortcuts—to include the
—enable-user-scripts switch after the executable path.
Now you can start using Greasemonkey scripts in Google Chrome—although keep in mind that not all of them work, since Chrome hasn't implemented all of the features yet. Once you've saved a Greasemonkey script into the User Scripts folder, simply refresh the page and it should work (or not).