A7A266 is a good mobo, and your 900 will have no problem going 1000, even without multiplier unlocking and core voltage increase, which the board does not support very well.
Actually, most Tbirds can run straight at 133 MHz FSB, your Tbird 9x100 will run 9x133 = 1266 MHz, may not be too realistic, but increasing the FSB by mere 12 MHz will get you past 1000, which the board will easily support and you wont be stressing you CPU too much.
For more overclocking info, you can browse this very section of THGC, you will find a number of threads very informative. Not only tips and howto's, but you will also know the pitfalls and ceavets in overclocking AMD and Intel processors as posted by posters who have actually done it!
Best of luck.
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