Upgrading from Tiger.

1. Yes. OS X Lion is currently only available from the Mac App Store, which is only available in Snow Leopard. Before you can download and install OS X Lion, your computer also needs to be on 10.6.8.

So you will need to buy and install Snow Leopard, download all of the current updates to be up-to date, then download and install Lion.

or

You can wait until sometime in August to just buy the USB Thumb drive from an Apple Store and just perform an upgrade from Tiger to Lion (at the moment, I am not positive if this is even possible).
http://www.macrumors.com/2011/07/20/apple-to-sell-lion-on-usb-thumb-drive-starting-in-august-for-69/

2. The contents within your iTunes will remain the same, though your iTunes will be upgraded to 10.4 in the process.

3. If you perform an upgrade, then your files will not be deleted. If you decided to perform a "Clean Install", then you will need to back up your Data beforehand.

 

My files were all exactly as I left them. The desktop is really just another folder so its contents should remain the same and look the same after the upgrade, unless you do a clean install.

 

Make sure you have 2GB or more of RAM. You don't want to get home, upgrade to SL and then find out you can't install Lion because you don't have enough memory. =P

 

Yup