I guess it depends on where you buy it. If you go to a Apple Retail store, yes. My dad's going this Saturday to pick up a new iMac C2D 24" and it will have Leopard. Most Apple Reseller stores should have it too, it'd probably be best to call the store you are planning to go to.
Your local store most likely won't have systems with Leopard pre-installed for a few days. What you'll get instead is a "drop-in kit"; a Leopard disc, basically. It'll cost you about an hour worth of waiting
No. They will include a Leopard DVD with the mac purchase. As stated on other threads, you'll have to wait for to clear out the channnels of Tiger installed macs. Estimated time this will take: 3 weeks to 2 months.