Buying a copy of Twisted Metal on Valentine's will give you access to classic Twisted Metal Black. Inside the box of the first run of games will be a voucher code for a digital version of Black, presumably with trophies and updated visuals akin to other HD makeovers.
Of course, this is unlikely to be the only incentive for buying new; expect an online pass to be included in the game based on Sony's comments after Resistance 3 was released or prepare to buy a new pass for the tune of £7.99/$10. It's a shame really, it would be nice to see more developers reward first week buyers instead of hitting them with the pass system, but as it is this whole deal will probably come off as a little bittersweet.
The Twisted Metal Black version available for download will be the proper game released in 2001, not the online freebie which came with the PS2 network adaptor.