I saw this on the frontpage here:
Basically, same type of mod. You play as the police and get into pursuits, arrest people etc. Since it was posted a few days ago I assume this mod is compatible with the newer script systems and stuff you need for GTAIV.
If you're running GTA IV on the latest patch (v188.8.131.52), there's a script mod available that can add a whole new dimension to the game: LCPD First Response.