As I said to Zaecus, it seems terribly unethical to me to take a job intended to be permanent with the intent to leave it in a few weeks, just in the abstract, never mind the personal involvement. If nothing else it will reflect badly on me in the future -- "she doesn't stick with her commitments", they would no longer be able to give me a good reference (and it's the bulk of my job experience up to this point), etc.