As it stands, the only way to get BlackBerry 6 is to purchase a Torch 9800.  That said, RIM plans to bring the new operating system to other devices in the near future.  While they couldn't give us exact dates (a large part of it depends on the carrier), they had a demonstration table with the Curve 9300, Curve 9330, Bold 9650, Bold 9700, and Pearl 9100 running the new operating system.

Take a look at the gallery of devices running BlackBerry 6!