No telling whether the future models will have 2 drives in them and no the E1705 can't have 2 drives in it. Just plug in an external. A 200gb 4200rpm would be piss slow. I'd wait to get one until they are atleast 5400rpm.
Not sure about the BIOS update but I do believe you should be able to jsut drop the Core 2 in without issue and as always, you definitely will need some thermal paste.
All the deals are out now. There of course are other discounts for Dell that you can find at places like www.gotapex.com. But don't expect something like 20% off of XPS systems.