Ahh, the old "ABS" (Action Battle System).

http://www.skytowergames.net/tutorials/abs.rtf (Downloadable text file)

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http://www.gamingw.net/tutorials/663 (part 1)
http://www.gamingw.net/tutorials/670 (part 2)

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http://www.gamingw.net/tutorials/386

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Basically, I'd say to read them all and take what you learned to make your own. Or just follow the instructions directly and edit it to fit your game.. whichever is easiest for you.