you should be fine with the i386 - esp. if you're a newbie. redhat and other major distros are concerned with making packages that will work as painlessly as possible on as many different computers as possible - the i386 arch will work on any later intel-compatible machine.
if you want a i686 specific linux box, then you'll probably need to go the linux-from-scratch or gentoo method. neither is particularly easy, and not recommended, esp. if you're just starting out. in short, just get redhat installed, play around with it, and go from there.