Even in Flash you'd need some form of programming skill, i.e. ActionScript.
Best thing would be to learn a programming language and develop programming skills. Than, with practice and hard work, you'll be able to make your RPG.

Yes, an RPG can be developed in Flash. In fact, at least one already has been. This can be found here.

Before you want to even start learning how to program in Flash(if you don't) you can develop a Design Document(if you haven't). Design Documents are great because they help you plan out what you want to do and how you want/have to do it. These nifty little documents can save a truckload of time even for an experienced programmer and can be used to 'poll' the popularity of your game. Some things on design documents can be found in Gamedev's Articles section which is here.

If you don't have any programming skills and don't want to learn any, you probably won't be able to make much of anything no matter what you are using. In that case, I would recommend just learning how to use a level editor in a game that you own and enjoy. Neverwinter Nights is a good one. But folks must own the game to play any levels you create. I guess another option would be to use rpgmaker or something similar. If you are going for a web-based media, you are pretty much out of luck. You can support multiplayer with the level editors, but the game is not going to be playable in your webpage if that's what you're going for.

EDIT: I used to have lots of fun making "rpg" games with the Age of Kings scenario editor. It's a real time strategy game, in case you aren't familiar with it. It doesn't have any rpg elements beyond hitpoints, but you can "emulate" them, so-to-speak. It's great fun.