You can not do that - if some can do that, is very easy to load a web page, and "format" your registry. Of cource you can always create a browser client plugin, but users not let it run and get a lot of waring that even make them go from your page.
Try this aproche - place a cookie on your client, and connect that cookie with a table on your local database, and the setting of your client. Then every time you see that cookie just load the settings. If the cookie-data not used for some months, then delete it.
If the data is personal and private, you must also create a login for your users.
If your customers are controled by you - and you can force them to use google chrome, you can also use the google gears for gogole chrome
http://gears.google.com/ that can store data on the browser.
Samples of Database stored on clients browser using javascript.
http://code.google.com/apis/gears/sample.html