crb: Yes, one tempo a week would probably be fine. A question, though: is this for your own running or for a team such as a high school team? I'm just curious.
to usetobe: I see the progression of phases for 5k-10k-type training like this (i'm basically rehashing Daniels' book here):
2-introduction of fast running while building lactate threshold
3-heaviest load of workouts, mostly focusing on vo2max sessions. these are the hardest on your body and hardest to recover from.
4-backing off the intensity with threshold being a focus and some quick stuff (reps) to keep the legs fresh. Along with a slight decrease in mileage, this allows for more recovery and allows one to come into "peak" shape for the most important races of a season. Basically, the point here is that it is easier to maintain fitness gains than it is to gain fitness. These workouts are meant to maintain fitness and allow plenty of rest/recovery so that the athlete can run his/her best then.
Having said all this, I am not the biggest fan of the ACTUAL workouts listed in the book. Some of them I like, some I dont. But the PRINCIPLES still apply. Check out some of the workouts on flotrack (specifically Ian Dobson's). It looks a LOT like a Daniels phase 4 workout - 2miles T, followed by something like 600, 600, 400, 200 (i dont remember exactly) at what I assume to R or maybe the 4 and 2 at F pace.