Ooh, ENTP and INFP combo! One of my favorite co-managers in my office is an ENTP, which is odd because we are really extremely different, but we appreciate the differences. So there's where I'd start: appreciate the differences. INFPs and ENTPs are both great at seeing the big picture, generating new ideas, intuiting flaws in the system that could be improved (albeit, I think mostly ENTPs are focused on the impersonal factors of the system while the INFPs focus on how the system is affecting people). Where we are very very different is the logic factor ... I understand logic, I can use logic as well as any T, but it's not where I come from ... I come from the people perspective. Any problem, any solution, any change flows through my filter of how is this going to affect people? My ENTP friend almost never sees things that way but again, he appreciates I bring a different point of view to the analysis.
Like others have said, let the INFP have time and space to get his/her work done independently and quietly. Don't assume because the INFP is quiet and not saying anything that nothing is going on inside the brain; nothing could be further from the truth! And don't assume because we need lots of time to ourselves that we don't like you ... we just need that quiet space to give our best.
I come up with many many ideas and love running them by Ts because you can easily see the flaws in logic and send me back to the drawing board; ENTPs also can see the good parts of the idea and suggest more logical/effective solutions which make the idea way better. Try not to judge your INFP colleague as being a flake if they come up with flaky ideas ... sometimes they will and sometimes they will come up with brilliant ideas. If the idea is flaky, let them know but in a kind way.
I think one of the biggest challenges with ENTPs is often you guys are the smartest ones in the room (and you know it) and you have little tolerance for stupidity. If an INFP thinks you think they're stupid, they will close up shop with you emotionally and you'll get nothing from them. They might smile at you and cooperate, but you'll never get their best or even know the richness of what they're thinking/experiencing.
Best of luck! I think you and your INFP can get along swimmingly with mutual respect and consideration!