How can I lock Mail/Contact/Calendars in an iPad? All members of my family use the iPad primarily for browsing the Web or playing games.  It is basically a living room computer. But I use it also for my e-mail. 

I know The iPad can be locked with a passcode as a whole (which I don't really need, because anyone who makes it to my living room is welcome to use it), but I would like to lock only the Mail app.  Is there any way to do that?
Without jailbreaking, I believe your options are the use of apps that provide this kind of lock functionality built-in, unless Apple decide to implement some kind of multiple user support in future iOS versions for devices like the iPad. 

I've previously come across Secure Gmail or Secure Webmail (there may well be others) which provide passcode protection schemes when starting and, judging by the screenshots, appear to be frontends to the relevant webmail pages (as opposed to a native application like the Apple Mail app). I've not used either, but they may be of use to you.