I answered your PM with some more specifics regarding the running. If you shoot Desert Dude a quick PM, he’ll usually give you some quick advice on the cycling and swimming side of things (as well as the running).
In general, assuming an athlete already has a solid fitness base of miles (which you don’t), I’ll stucture the training plan with two things in mind.
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The athletes fitness and ability
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The race distance they are training for
This post goes into a little more generic detail:
http://forum.slowtwitch.com/...t_reply;so=ASC;mh=25
On there I show this table that helps illustrate the type of training that you do and how it relates to fitness for different events.

As you can see, if your race consists of only 11 minutes of running (ie 1-2 mile stand alone race) you would want to do a healthy mix of Vo2max interval training, a good portion of speed work, and some threshold training mixed in there, while still having the bulk of your training be aerobic running. If your race is 60 minutes long (10K-15K stand alone) speed becomes much less significant, V02max has less focus, threshold training becomes much more important, and aerobic running increases. For iron distances its almost all about aerobic training (except for fast IM athletes).
I’ve broken this down into table form. For you I’m going to assume this run segment (4 miles) will take you ~30 minutes to finish. Look at the table:

Look at the top table and slide right to the 9th column (29 minute tri run). Here I recommend (ball park numbers) 0.7% of your total running to be speed work, 4.7% to be intervals, and 8.7% to be threshold training.
So, lets say you are running 25 miles a week, comfortably. I would knock that down to about 22 miles a week because you will be adding intensity, and do the following on a weekly or bi-weekly basis:
EDIT: I make an adjustment for triathletes by dividing total mileage by 0.8 before calculating. This takes into account the extra load placed on the body through cycling and swimming. Adjusted value would be 22/0.8 = ~28 miles. Then I mulitply 28 by 0.007, 0.047, and 0.087 to get the following distances:
300 meters of speed work
2100 meters of intervals
2 1/2 meters of threshold running
From here there is a little bit of art involved. I’d probably suggest doing a 2.5 mile threshold run every week. However, the second workout I would alternate between one easy session of 3 x200m pretty hard one week and then the following week would be 5x800m @5K race pace with 400 jogs.
The idea is that if the training load is too easy, then you bump everything up in proportion (everything is 5% longer). If it is too difficult, then you bump it down in proportion.
Oh, and back to the original question: How far? I answered this in your PM. I typically like to do short, medium, and long runs. 3 short, 2 medium, 1 long, and 1 short or a day off. Mediums are twice as long as the short. Longs are three times as long. With this forumla, the long runs tend to be close to Jack Daniels’ 25% rule. The reason why I write it this way is because many triathletes only run 4 days a week, and the 25% rule becomes kind of meaningless. For every day less that you run, you get rid of one of the short runs. So a person running for days a week might run a 2 miles, 2x4 miles, and then have a long run of 6 miles, for a 16 mile week. If the above 22 mile week was done on 4 runs a week, it would be 8 mile long run, two 5.5 mile runs, and a 3 mile run. The workouts would likely be done of the 5.5 mile days…but again, these are ballpark numbers. You need to adjust according to how you respnd to the workouts.
Edit: I originaly wrote 3 medium runs. It should be 2.