I expect you will see a service release the day of the consumer launch (Jan 30). Its already released to business (has been for a couple of weeks).

If you buy a Dell today you get it with XP and an express coupon for an equivalent update of Vista after Jan 30.

There are about 6-7 different "flavors" of Vista going from "home basic" to "ultimate" depending on your need. Most people will probably end up with "home premium" as it will be the most common upgrade step.

This is also the launch of Office 2007 -- this is a pretty interesting upgrade as well.