I'm playing on the XBox and I'd like to play two characters to experience different storylines and see how different races play.
Is this possible? I'd hate to have the saves of one character override the saves of another!
If you're not using separate accounts, quick and autosaves will overwrite each other, manual saves will not (unless you choose to save over another save).
By using separate accounts, the saves will be entirely separate, preventing any of the other person's saves being overwritten while playing.
When you "switch" between characters, make sure that when you save the camera shows the face of your character, and maybe some representative background. This way, you can easily tell to which character the save belongs and reduce the risk of accidentally overwriting the wrong file.
Using separate accounts would work, but seems like overkill.
I have many, many different Skyrim characters saved on my Xbox. The saves are arranged in descending order from most recent to oldest. So, if you make several saves with your current character, then you can't even see the other characters' saves on the screen when saving.
Autosaves and quicksaves are shared between characters, so make sure you do a manual save any time you're done playing.