[Ronster]

"regular old" fuel injection in this case is sequential port injection. gas is squirted into the intake manifold port towards the intake valve, hoping it mixes with the air enough to ignite evenly. DI puts the injector into the top of the combustion chamber so the intake draws in only air. fuel is squirted directly into the cylinder (hence "direct" injection) during the intake stroke and the mixing turns out to be a bit better. this along with variable valve timing and use of aluminum for the heads allows much higher compression ratios to be used. in the hfv6 di it's 11.3:1 specified with regular unleaded gas. the difference between di gas and diesel is that this engine still uses spark to ignite the fuel/air, whereas diesel injects the fuel during compression for compression-ignition which requires much higher pump pressure. even so, the DI motor requires over 1,000 psi (I believe 1700) at the injectors which means this engine has an added mechanically driven pump, on the rear of the left cylinder head. GM claims that pollution is reduced especially during warm-up.
there are several gm and holden websites that describe this in more detail. for instance see media.gm.com.
I should add that technically this is known as SIDI - spark ignition direct injection.
rg