OK, my experience is way different than most of the other posts.
We bought a potty chair around 12-13 months, just to have around. We told ds what it was but no pressure to use it vs diapers. Around 14 months he started asking more about the potty (with bits of interest throughtout the time since we bought the potty till 14 months). We encouraged the interest with naked time and talking about using the potty if there were accidents during the naked time (but still no pressure, the talks were very light hearted and just informative KWIM??). By 16 1/2 months he was using the potty all of the time during the day with diapers at night, by 18 months he used the potty full time. We had a few accidents after the diapers were gone, but they too were treated like it was no big deal but he was reminded to use the potty (he got pretty upset when he had the accidents cause he really liked (and still does) using the potty ~ so we'd be sure to tell him that it was OK and everyone makes mistakes and has had accidents in their lives, etc.). Since then he has been going strong with only one or two accidents.
I know this is early (and not typical based on many of the reactions we have gotten (Ds turned 2 in November)) but I just wanted to let you know that it is never too early (I gained this opinion after reading some of the elimination communication (EC)threads around here). I think as long as there is no pressure then it is fine. The combination of having the potty, seeing Dh and I go (he really loved to watch his dad go especially, and outside he thought was really awesome to watch!!!!) and the naked time ~ I don't think we could have gotten there without the naked time, it lets them see how their body works I think, worked really well for us.
Oh and we bought some really great training pants from ecobaby.com, but he really didn't need to use them, so I'd shy away from that (but each kiddo is different!!).
And the other thing that did help us was prompting him to use the potty about 15-20 minutes after eating or drinking a big drink of something (I'd just ask if he needed the potty and he'd say yes or no ~ I got this idea from the EC threads also ~ I'd definately read up on this cause a lot of the info I saw can apply to the older kids too!)
Best of luck to you in your potty using journey!!!!!!