1.)Look above, that will cover you, with these comments as well. Delta's 727s will be gone no later than 2005-2006. Their L-1011s will be gone by April. Delta has numerous 737-600/700/800s all on order, as well as 6 B-777s on order. There is speculation that Delta will place a huge 777 order soon.
2.) ATL is their primary hub. Service to NRT, LGW, CDG, FRA, ATH, Istanbul, FCO, etc. and pretty much every major North American city (minus YVR). Also is their Latin America gateway.
CVG is their second largest hub, and is primarily used for Northeast flights to the rest of the US. A few international routes to FRA, CDG, and LGW.
SLC is Delta's Western hub, which they are talking about closing down shortly.
DFW is Delta's 4th largest hub, and they fly to the largest US cities (JFK, BOS, LAX, LAS, etc.)
JFK is Delta's international gateway, with flights to Europe, Africa, and soon Asia and South America.
Other major cities:
Boston - International gateway eff. June 1, 2001 with flights to LGW. Serves LAX, LAS, DFW, JFK, LGA, DCA, ATL, CVG, Bermuda from BOS.
LAX - Largest operation on the west coast (not the rockies). Serves ATL, PDX, CVG, BOS, JFK, DFW, LAS, MCO, etc.
MCO - Delta Express' hub. Mainline goes to ATL, SLC, LAX, and others.
LGA - DL is building up AC Jet from LGA as the RJ expansion booms there.
Air Canada (starting soon)
Air France (SkyTeam member)
AeroMexico (SkyTeam member)
Korean Air (SkyTeam member)
Is seeking a 26% stake in Air India with Air France
Will buy portion of CSA, CSA will join SkyTeam soon.
Owns Comair and ASA. Has stake in SkyWest (connex carrier). I don't know about AC Jet.