Just some additional thoughts from an IDPA newb:
If you have a .38/.357, (that's under 42 oz.) it plays in "Stock Service Revolver" class and can be reloaded with speed-loaders but not moon-clips. Ammo has to make 125,000 power floor, which can be an issue with some factory .38 Spc. (That's velocity times bullet weight, so 125 gr. bullet at 1,000 fps, or a 147 gr. slug at 850, etc.) Most guys are using the Safariland Comp III type speed-loaders.
I understand many local club-level matches seem pretty chill on the PF requirement, especially for newbies like me. In my case, I show up with standard Walmart Winchester ammo and nothing is said (obvious creampuff may raise some eyebrows, though). It's been made clear to me that in actual sanctioned events, it's a different story, however.
I've been using CompIIs, and they work fine. I was interested in speeding up my reloads, though, so (in addition to a whole lot of practice) I bought a compIII. I don't know if I got a bad one, but it actually
slowed my reloads because it took a fair amount of wiggling to get the rounds to release. I've since bought a jetloader, and it's terrific. I can highly recommend them.
You'll need a belt holster that covers the trigger and is of a standard "concealed carry" style. No space-gun skeleton holsters with crazy offsets etc. You'll need a way to carry 3 reloads as well. And a vest or other cover garment.
A cover garment can be anything that conceals your rig. Even a long shirt, or a jacket, so there's no need to run out and buy a tactical vest if you don't have one.
As far as holsters, "standard concealed carry" doesn't necessarily mean tight-fitting leather with a retention strap. Kydex holsters are very popular. They may be "gamer" holsters in that I wouldn't use mine for everyday, but they retain the gun good enough for combat action shooting matches. I much prefer them over a standard carry holster. Plus, at least at my match, if the holster does have an external retention device (e.g. strap), it must be employed, which seriously slows my draw.
As Sam1911 point out, what
is important is that the holster cover the trigger.
One note on speedloader pouches, though: If I understood the rules correctly, if you use an open-top pouch, they must cover the body of the speedloader.
Thus, these Blade-Techs are legal:
http://www.blade-tech.com/Speed-Loader-Pouch-with-Belt-Loop-pr-835.html
...Whereas these Safarilands are not:
http://www.midwayusa.com/viewProduct/?productNumber=546826
Personally, I'm kind of odd. I shoot both SSR and ESR with a 4" 629 shooting .44 Spc.
I've always thought that'd be a dandy SSR rig. One could shoot some real soft handloads and still made SR PF.
My own personal rig is a (DAO) 4" 686 with Miculek grips and FO front sight. BladeTech holster and speedloader pouches, and jetloader speedloader (though I still use my compIIs are backups). I do reload, but I'm relatively new at that as well, so for now, I shoot 130gr WWB for the matches. the handloads I've worked up for SSR, though, are 4.2gr W-231 over a 158gr Berry's plated RN (1.475" OAL), with a moderate taper crimp.
With all this said, though, the ethos of IDPA is to use everyday equipment. If you already have a revolver and a holster, you're most of the way there. Just show up, be safe, and have fun!