How soon can I file my 2007 taxes?

I heard that at around this time of year if you go to h and r block or amscot you could use your last paystub to get an advance (refund anticipation loan) before you get your W-2 in Jan.? Has anyone done this or tried to do it or does it just sound bogus? Someone told me they did it for christmas money but if you really could then dont you think everyone would????