Bodgit, Jeff is right. The only real way to quickly improve your swimming is to have lessons.
A half hour lesson normally turns into at least an hour as the teacher will give you drills to do once he has gone, and half an hour once a week will be very cheap.
Books and videos are great once you know what you're doing but useless to start with as you won't be able to feel whether you are doing the drills properly or not.
(I managed to get from being very below average swimmer to comfortably swimming Ironman last year in 70 mins having had a half hour lesson every week for 4 months, and three other practice sessions per week).