There is a huge amount of technique involved in swimming, that coupled with the fact that - as you mentioned - it takes time to get ready can make it a bit of a hassle.

When I started I couldn't swim a couple of lengths before I was knackered.The 2 huge helps that sorted me out were;

1. I started going along to a Masters class in which you start in a lane & position graded on you performance & then follow a structured session. This is sort of like doing a club session were you might do a warm-up, build, main session & cool-down. It really helps to have people around you & there should be an instructor who can give you some pointers.

2. I was given for Christmas a DVD set of SwimSmooth dvd's;

http://www.swimsmooth.com/

people also swear by Total Immersion;

http://www.totalimmersion.co.uk/

TI may give you a great smooth stroke, but some triathletes say that this does not transfer to rougher open water swimming very well.