Hello World,
The encrypted wallets are in the 0.5.x code only. This is still in beta and hence not on the multibit.org website.
There are installers you can download directly from:
https://github.com/jim618/multibit/downloadsIt is not quite ready for general release yet. If you have a read through the readme.txt and make sure your wallets are backed up by exporting your private keys you should be fine. I have been using it with my real wallets for the last couple of weeks but at the moment I am advising people to use it just with small amounts (just as a precaution).
The help has been redone for almost every page so that should explain the new functionality. You can see the help in MultiBit using 'Help | Help Contents' or go here:
http://multibit.org/v0.5/help_contents.htmlIf you have any questions or spot ANYTHING unusual let me know.
Jim