Adding on what SarahK said (well put, btw), you also want to make sure all programmers understand and use basic standards for their code. Using standard naming conventions, consolidating common function calls, includes, etc. can make a huge difference in the way people's codebits work together.
Set expectations about communication among team members as well. If it's daily meetings on ICQ for a few programmers working on common issues, or face-to-face weekly meetings of the entire team, make sure it happens, and make sure it's meaningful. The one thing I've seen doom a project is that everyone gets their assignments, and they all scurry into their corners, working until the project's done without any support or communication. You end up with a lot of nice code that doesn't fit together into a solid, workable solution, and then the culling begins.
I got an idea from an actor friend of mine who told me how actors get together and do a 'read-through' of a script before heading out to study their parts. Taking her description, I implemented a 'spec read-through' for the programmers I supervised, and was amazed at the questions and flow of ideas generated. I was also amazed at how some of them had never had this kind of meeting before.
Programmers got up and talked their ideas through using whiteboards with input from the others, and it really made a huge difference to the end product. It also helped me formulate all the questions I had for the spec writer. Once we started it, we kept it up through the entire project - the programmers remarked that it helped tremendously.
Also to emphasize another thing SarahK said - you need strong technical and project management. If you're the one tagged as "Project Manager", I highly recommend reading a few works on solid project management skills. If you're the Technical Lead for the project, talk through with the Project Manager what s/he expects of you (and vice versa). If you're in both roles, don't neglect the PM work in code crunch times. It can make a difference in your level of sanity at project's end, trust me.
Best of luck!