A few important things to consider:
Processor: You want at least a pentium 4 3 ghz
RAM: You want at least 512 mb of ram
Hard Drive: At least 80 gb
Get a cd / dvd burner
Operating System: XP Pro preferred but XP Home should suffice.
Think about warranties. You should get at least a full year, and some carry 3 year warranty.
Get at least a 17" flat panel monitor.
I am not too big on brands, but the ones you've heard of are probably safe. If you can get the above options for the cheapest price, then you probably have done well
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