I had heard that he was involved, but I believe the movement for liturgical reform was underway at least by the 50s, before VatII. (Lucile Hasley mentions it in an essay from that time, and we were learning sung "responsorial psalms" in school by '58.) I expect different people for reform/"reform" worked and hoped for very different things. I would find it difficult to believe that Ratzinger was ever a contributor to the self-glorification that other posters have mentioned (which seems to be fading in recent years, though not enough).
The liturgical reform movement has actually been underway for quite some time, and there really (IMHO) was a need for a limited sort of reform, consisting mostly of making the priests actually celebrate the mass properly (instead of doing the 12 minute low mass "celebrated" in a buzzing whisper with the altar boys bobbing so fast they looked like ducks). Certainly, there were other things that could have been cleaned up, too, and I didn't object to things like the "dialogue mass," the people saying aloud the prayers normally said in response by the altar boys and those parts that had originally been meant for the entire congregation to say. And I also liked the priest's prayers being said audibly and intelligibly, because they are very beautiful and meaningful liturgical prayers.
But somehow the whole thing just escaped. There's a good article by Fr. Brian Harrison in this month's Latin Mass Magazine, discussing this very fact. Most bishops surveyed before the council either were not interested in liturgical changes, or were in favor of very limited ones (such as the above, which were stylistic and not changes to the essential liturgy). A very tiny percentage was in favor of radical changes - yet somehow, he points out, only three years later, this tiny group of "liturgical leftists" somehow got through a program for sweeping changes that were much more dramatic than anybody had expected. Once these changes were obediently accepted, they were followed a couple of years later by another round of changes (including the removal of altar rails, Communion in the hand, the Mass facing the people, etc.) undreamed of by even the earlier group of liturgical leftists.
I don't think Ratzinger was a contributor to this last phase, certainly, and obviously many people, no doubt including Ratzinger, who were involved in the first part of the "reforms" had any idea of the extent to which such "reforms" would be carried only a few years later.