Google has released a Gmail gadget for Google Desktop Windows users. This gadget allows you to access Gmail in Google Desktop. You can rum multiple instances of Gmail gadget if you use more than one Gmail account.
This is not a full featured app, but it allow you to do read, and compose mails, star messages, search, keyboard shortcuts etc. While reading and composing it pops out of the sidebar and doesn’t use much space.
Gmail gadget is only available to windows users at the moment and requires Google Desktop version 5 or higher to run. Another option is to use GMDesk to access Google Apps on desktop