I'm well and truly addicted to Triathlon. It doesn't need to be expensive, though it is very easy to be drawn into kit to speed transitions etc…
mtb with slick tyres, some tri-shorts, goggles, running shoes… and that's about what you can get away with. use a bike jersey on the bike & run. The first two I did, I wasn't too bothered about transition speed – I was more interested on being quick in the actual swim/bike/run bits. Transitions are sped up no end with a tri suit… but I didn't want that expense back then.
I would highly recommend going to a running shop and getting some shoes for you – I didn't enjoy running until I got some well fitting shoes, and now really enjoy it.
Swimming – lessons at your local pool are a good way to get the basics, but most tri clubs cater for beginners as well, and usually have swim training sessions, again, catering for beginners all the way through the ranks.
freeform – what was your event?
I've got one more pool based Olympic distance (800m pool swim) before I enter the world of open water olympic – Dambuster in June! eeek.