Requiem aeternam

On Tuesday night I went to the Opera House (no prizes for this pic!) to hear a variety of organ and choir music featuring Duruflé's Requiem. I've often been attracted to requiem pieces before (heard Mozart's a few years ago, also in the SOH and own a few CDs, including Duruflé's). On Tuesday night I was struck by the most obvious feature of the entire experience: the repeated (and then repeated and repeated again for good measure) supplication: Requiem aeternam dona eis - 'Grant them eternal rest'.

Now leaving aside the whole prayers for the dead thing, it got me thinking about 'rest' as a category of biblical hope. Certainly it has ample scriptural warrant as a prominent OT theme (e.g. Gen 2.1-3; Ex 20.8-11, 33.14; Josh 21.44; 1 Kings 5.4; Ps 95.11) picked up in the NT (Matt 11.28-29; Heb 4.1-11). But when is rest? Are the faithful dead already at rest? Certainly the common gravestone acronym 'R.I.P.' seems to assume those who now sleep in the dust are at rest. But are they not also waiting, like the, er, rest of us, for the resurrection of the dead?

But back to requiems: does anyone know what the Roman Catholic position is on this matter? Are the faithful departed for whom the requiem is said/sung already assumed to have entered their rest, or is the requiem a prayer for the successful navigation of the final judgement such that requiem aeternam is achieved?