Yes it is. Ignore all the bullsh1t that piles up in mags like runners world or gays health, just keep it simple 1 min fast, 1 min slow (some are saying 2 mins slow nowadays) and repeat as many times as required. Work like hell on the work interval and don't entirely mong it on the recovery. Also try it on hills.
Interval training is an excellant way of improving your running speed. Also your metabalism continues to burn calories at a much greater rate after interval training as opposed to long slow runs.
You should start off slow (as ever!) 1min run 2 min walk or go for distance if improvment in speed is your desire.
Bob Glover has written some excellent books on running.
For all you hardcore try 20 seconds as hard as you can then 10 seconds active rest and repeat until you have reached 4 mins
Running 2, walking 1 is a good way to build up your distances if you are not used to running and unfit. You can gradually increase the length of the running portion until your happy running for 30 minutes straight and then move into a more traditional running program.
This is different from hard interval training where the intention is (obviously) to work hard during the interval. This type of training is phenomenal for building fitness. You can alter the work rest intervals as you like, variety will likely improve your results and certainly be more interesting than sticking to a single routine.
As far as ratios goes I would recommend anything from 3:1 work rest through to 1:3 work rest. Obviously the more rest you get the faster you will be able to go during the interval while shorter rests will teach you to deal with cumulative fatigue and help you recovery. This is detail however the inclusion of any interval training will greatly improve you fitness.
It's very effective. I'll usually do 2x45-60min sessions myself each week, alternating every minute or two between a fast walk, jog, and 3 quarter sprint. See if you can find a route that throws in a couple of hills aswell. Goes a long way in improving your time for 2.4km runs also.
If you're a fat bastard like me you'll also see the weight fall off if you apply yourself