23 October: A new Formula 1 qualifying system for 2005 has been approved by the FIA and the F1 teams. The new qualifying format comprises 2 single-lap sessions run on Saturday afternoon and Sunday morning with the times from both sessions aggregated. The order for the Saturday session will be in reverse order of the finishing position from the previous race while the order on Sunday will be in reverse order of the Saturday session.
There will be no restrictions on fuel for Saturday while on Sunday qualifying will be run on race fuel load.
This new format aims to provide spectators with a chance to see the cars run on low fuel loads on Saturday and fill in the empty morning on Sunday.

Formula One World Championship - FIA Press Release

Following votes of the FIA World Motor Sport Council and the Formula One Commission the following qualifying system will apply from the 2005 season.

Two sessions The first from 1300 to 1400 on Saturday; the second from 1000 to 1100 on Sunday. The first session is single lap qualifying, with the cars going out in the reverse order of their finishing positions at the previous race. The second session is also single lap qualifying, with the cars going out in the reverse order of the qualifying on Saturday (i.e. the fastest car on Saturday runs last on Sunday).

The cars run on Saturday with unrestricted fuel. They go into parc ferme after this qualifying session and for the Sunday qualifying session they run with race fuel, having been allowed to refuel before the second qualifying session, but are not allowed to refuel again before the race starts.

The times of the two sessions are aggregated to determine the grid, with the shortest aggregate time in pole position.

Check out the Formula 1 Regulations Page