I would sprint say twice a week. Two really good quality speed sessions with time to recover between. That's what the slower jogs are for - to help you recover and get a base level of aerobic fitness. Sprinting is more anaerobic but it will produce more lactic acid which your body needs a chance to get rid of.

You can put one moderate pace run in per week also. Top sprinters have only a couple of really hard speed sessions a week so I think that's the way to go. It's definately not a good idea to have your speed sessions too close together - have a couple of days of other training and maybe also a day off between them.