In reply to RCJ:
I did my first super-sprint (200m, 20k, 2.5k) earlier this year. I'm a regular salad dodger (15st) but otherwise healthy.
I did the swim bit breaststroke. Didn't know how to do the front crawl properly, so didn't even try. Did no swim training at all beforehand.
My bike was a £250 halfords hybrid (replaced the MTB tires with 1.25" road tires). Training consisted of occasional 10k (and one 20k) rides around Saddleworth (a bit hilly).
Running involved an old but decent pair of trail running shoes (that I normally use for hiking). I'd been doing some running since Christmas of varying lengths, but mainly <5k.
Came in at 1h 11m, which wasn't bad going considering. I've got my next one on Sunday, and I've even learnt how to swim front crawl (badly).
Turn up, register, play nicely with the other children and have fun.