thinktank

I'm looking for recommendations on document management/CM systems for
managing mostly Office documents. We need to manage this process just
like checking out code, where each change will be reviewed by someone
before it can be checked back in. Anyone have any suggestions? At VZ we
used good ol' Pegasys and Perforce, but we have limited school funds and
need something cheap but good and user-friendly. I would even consider
something open source as long as I can convince our Director :-)