Edited from from the Metal Gear Wiki:
Metal Gear Saga: Volume 1 is a bonus disk that came with Metal Gear Solid 3: Subsistence when the game was pre-ordered from participating retailers.
The disk contains information about the Metal Gear history from the start and upto the "present day". There is also information about Metal Gear Solid 4 and new information about characters that has previously been unreleased. There are also several interviews with Hideo Kojima where he discusses Metal Gear Solid 4, among other things, such as the non-canonical Snake's Revenge.
The information about all the Metal Gear games are all put together in chronological order, making up a 30 minute "documentary" split into five chapters.
-Chapter 001: Metal Gear Solid 3: Snake Eater
-Chapter 002: Metal Gear
-Chapter 003: Metal Gear 2: Solid Snake
-Chapter 004: Metal Gear Solid
-Chapter 005: Metal Gear Solid 2: Sons of Liberty
The DVD also contains trailers produced by Kojima Productions.
-MGS4: Guns of the Patriots (E3 2005)
-MGS4: Guns of the Patriots (TGS 2005)
-MGS3: Subsistence (E3 2005)
-MGS3: Subsistence (GC 2005)
-MGS3: Subsistence (TGS 2005)
-Metal Gear AC!D2 (E3 2005)
-Metal Gear AC!D2 (TGS 2005)
Metal Gear Saga: Volume 2
Metal Gear Saga: Volume 2 DVD is a bonus disc that comes with MGS4: Guns of the Patriots when the game is pre-ordered from participating retailers. Where Volume 1 is a chronology of the games so far, Volume 2 is an in-depth look at the games central 'Snakes'. The chapters for this 25 minutes documentary are:
-Metal Gear 20th Anniversary
-Liquid: The Second Snake
-Solidus: The Third Snake
-Solid: The First Snake
The DVD also contains the remaining MGS4 trailers produced by Kojima Productions.