Sure can. go into your camera, hit the application/menu button then go to options...once in there you will see all of the camera settings...flash,white balance etc...etc...go down to where it says store pictures it will say Device Memory/On Media Card, change to Media car of course then scroll down and select what folder on the media card, I believe it defaults to Media Card/Pictures, but good to double check...hope that helps ya
What storage are you referring to I can only think of a few things that maybe using your device storage other then applications, example: Bluetooth transfers of files (which it asks you where you want to store), Camera (previously indicated on how to do so), music/video/ringtones/graphics (you control where you put these)...so if your referring to the media card storing application data and files..no their is no way to make those store info on the media card.
Bla1ze is right. But, in regards to your email, change the settings (messages / menu options / general options / keep messages) to 15 days. You really don't need more than that, since you can still access them in your email client (Outlook, Lotus Notes, etc, etc). Also, every so often check the remaining memory on your device (options / status). Having low, or no memory is what causes the device to 'delete random items'...