2.7 ghz should be sufficient, at least for a while. You might want to think about upgrading next year, and I suggest getting another 512 mb of RAM. Unless you already ordered the card, I would highly suggest spending at least an hour or 2 shopping. There are many good deals to be found if you just look long enough! Did your power supply come with the case? Maybe you could look at the case to find out. There is a program you can download that tells you the specs for your system, not sure if it would tell you the information about your PSU. The power supply itself might be labeled with it's power. Shelling out the extra 50 USD for a good power supply is a good idea though, just to make sure! (500W+)
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