If you're new the triathlon DEFINITELY do one the the Thames Turbo ones - go here to enter on-line. Cheap as chips compared to all the big name events too.
We run 4 events on the morning of each bank holiday monday. There are still places available.
The swim is in hampton open air pool (12 lengths, circa 430m), first swimmer off at 7am. Swim is in two waves and is seeded so there's as little biff in the water as poss - you just need a reasonably accurate 400m swim time.
Bike is a pan flat course (21Km) and the run is a pan flat 5Km trot around Bushy Park. Atmosphere is friendly and NOT elitist.
Swim: Goggles and either a full tri suit or at the very least padded tri shorts (no nudity in transition) so you'll be wearing whatever you swim in. You could do speedos and pull shorts over them in transition.
Bike: Bike, helmet, number belt*, shoes and probably 1 bottle of water. If you're not wearing a tri suit (all-in-one) you'll need a top of some kind. It can be cold so maybe gloves and a windstopper top too. *(number belt - buy one for a fiver or make one out of inch wide elastic with a plastic buckle then pin your race number to it)
Run: Running shoes, number belt
I could go into specifics of other stuff you could use, but if you're just wanting to have a go, you really don't need shed loads of kit. As well as the fast boys on TT bikes with pointy hats, LOTS of folk do the Thames Turbo races on hybrids or clunkers and still have a great experience.
The only thing you can't use is a fixed wheel bike, single speed is ok, but not fixed.
As far as training goes the club runs a free 2 week trial where you can try all the sessions (contact membership via the website). 1 core strength session, 2 swim sessions, 1 group turbo session, 1 track session, 1 group run (1-1.5hrs), 1 group ride (3-6hrs depending on time of year) each week.
(obviously i'm involved with thames turbo)