Quick DVI tutorial:
DVI-D means digital-only DVI.
DVI-I ("integrated") is DVI-D plus analog VGA signals.
DVI-A (analog-only) is not part of the DVI standard and actually shouldn't exist.
All of Apple's DVI ports are DVI-I ports, which can drive both VGA and DVI-D displays. (VERY few displays have DVI-I ports on them.) A DVI-D cable will plug into a DVI-I port with no adapter.
All but the most recent Apple machines have only single-link DVI, but only very few displays (like the 30" Cinema HD display) use dual-link DVI. Dual-link DVI is not two cables, but rather just uses all the wires in the connector (single-link only uses 1/2).
tooki