According to Gartner and also to the sales statistics published by IDC (Via AppleInsider) HP is still the leader in Worldwide PC shipments world-wide and also in the United States.

Overall there is growth again in PC sales in the 3rd quarter, which is interesting as Windows 7 has not even launched yet.
Apple is only in the top 5 PC vendors in the U.S. at place #4. In world-wide sales Apple is not in the top 5.

The top 5 vendors in world-wide PC Shipments according to Gartner (results still preliminary) are:
HP
Acer
Dell
Lenovo
Toshiba

The top 5 vendors in US PC Shipments according to Gartner (results still preliminary) are:
Dell (IDC sees HP at #1)
HP
Acer
Apple
Toshiba