Probably an older model with XP installed. You would still qualify for the Vista upgrade (assuming the machine meets the specs) until the end of March.
The Vista upgrade is by redemption (log proof of purchase on website, pay Postage and Packing and the disc will be mailed to you, not sure on waiting time for delivery)
Obviously the XP machines offer good value as they have to be sold soon-ish!
What was the model?