So what is the minimum required?

[JoeWilkinson]

I am not actually arguing for the minimum except in terms of introducing too much at once on 1st Sunday of Advent 2011.
It seems to me that in our parish, with the local compositional talent, we could (not should) use any of our current Lord Have Mercy/Kyrie & Lamb of God unchanged, also with a tweak that most of the congregation won't notice (yes really!) put God of Hosts into the Holy Holy. The Eucharistic acclamations need work - losing the "Christ has died"s for a start but the Doxology can continue as it is.
The Gloria can be postponed until Christmas - need to make a choice and prepare congregation at a time when Glorias aren't sung, but who said Rome was practical. Someone pointed out that we sing the chorus to "Angels we have heard" anyway on Christmas day so that is OK then!
So unless we get into singing Entrance Antiphons and Comunion Antiphons only the Gloria and EA's need to change. Or have I missed something?

[Nick Baty]

I am not actually arguing for the minimum except in terms of introducing too much at once on 1st Sunday of Advent 2011.

No need to wait until then. The texts have been allowed since Easter.

the Doxology can continue as it is.

Not quite – the words are different.

[Eastern Promise]

Oh b***er! Not the Doxology too?

[FrGareth]

Oh b***er! Not the Doxology too?

Only for the priest. I don't think the people's part has changed!

[FrGareth]

I am not actually arguing for the minimum except in terms of introducing too much at once on 1st Sunday of Advent 2011.

Assuming you are in England or Wales, the only new things introduced on 1st Sunday of Advent should be the 3 presidential prayers (collect, over gifts, after communion) and preface.
Your target is to begin singing the new Gloria, Holy, Acclamation (and your priest the doxology) effective early September!