Probably a silly question, but can you cast Mind Steal on a player who has no spells?

No, you need to hava a valid target (faq. v1.1 updated November 28 -11, page 2) and page 6 gives an example of an illegal spellcasting scenario: casting Nullify on a Character with no spells.

Thanks for the reply.

Now to persuade my friend who wants to house rule it so you can!