Version control and tracking

Hello all
Need a bit of steer.

We have to change a large number of assets - .gifs, .jpgs, .swfs.
We need a tool that we can use to:
- track what's been updated
- what they look like (preferably next to one another)
- whether they've been signed off

Does anyone know of a cheap system that would let up do this?
Or do we need to construct our own database (with various admin permissions - upload/view and signoff) which can display thumbnail, name, size, type, updated, signed off yes/no etc.

Any ideas?

Thanks.