I suggest you hold out a bit for a month or two. Prices will go down for current cards, and you might be able to trade-in your celeron system for a new AMD AthlonXP setup, cheap and fast, would unlock the high scores you expect and allow the cards to flex their performance. You might easily be able to afford this new card+CPU setup if you wait a bit. Otherwise you can do it now, but search well for the right price. I hear there are 56$ AthlonXP 1.4GHZ 1600+ CPUs, and since mobos are so cheap now, you can easily trade-in and save even more.
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Is the opportunity to earn money by working, free?