GamePen has posted an interview with Gearbox Software's Randy Pitchford, with Geoff Keighley asking intelligent questions about their upcoming official Half-Life add-on Oposing Force. Here's an excerpt with some info about the NPC interaction in the game:

Patrick, our programmer, has spent a good deal of time making the squad combat very fun in OpFor. The first big difference you’ll notice is that instead of just two NPC’s being able to follow the player, Cpl. Shephard can gather a whole squad together and bring them into action. Sometimes you’ll be able to talk to other soldiers over the radios you find scattered around the base and work out how to link up with them. Other times, you’ll come across a fight in progress and can jump in to help your team. We spent some time improving the AI so that the new larger squad of soldiers can act more intelligently. I hope that our programmers can spend even more time with it before release to make them even better at working as a group and avoiding damaging the player and each other.