Time to walk the walk

Forgive me if this topic has been raised before, but here goes: I was jogging around my favorite urban lake yesterday thinking about swimming (of course), and I decided that one thing I'd like to do before the end of the year is actually compete in a real live swim meet. I don't have regular access to an organized swim program because of my work schedule, but I'll happily take any advice on how to train. Currently I'm about 20 lbs. overweight, but I jog regularly and swim about 3 - 4 times a week. Thus far, all my swimming has been for the fun of it. Any ideas on how I should actually train for a competition? What kind of workout regimen, schedule, etc.? Now, I know that Masters swimmers are great, wonderful, supportive and not at all hostile to those of us who are complete novices. However, I would like to make a decent showing, even if I finish last in whatever events I swim. (Also, I don't know what meets are coming up at the end of the year, so if anyone has any clue on competitions in the Seattle area, that'd be swell.) I came up with the idea because I'm training for a 5K road race at the end of July, and asked myself why I "compete" in a sport I only marginally like, while I don't do the same in swimming, which I consider just about the most fun you can have with your clothes on. So to speak. Thanks! Adam