As it's not out until tomorrow, and Microsoft are coming down like the proverbial ton of bricks on anywhere caught selling it early, I'd not fancy your chances mate.
Had an e-mail from Play.com yesterday saying they had posted it to me, so I'm keeping my fingers crossed that the postie might have dropped it through my door after I left for work this morning.
If you're still looking to buy, I saw an advert for Blockbusters this morning saying they were going to be selling it at £34.99.
My copy has just been delivered from Play (to my parents though). Hopefully my request for having tomorrow off will be approved, so I can have a mini Halothon.