I've simply had many experiences upgrading many computers to Windows XP, and even when I've tried upgrading windows XP Home to Windows XP Professional I've noticed instabilities and slowdown. That was on a 1.7ghz Dell machine. I'm just saying its the best option, and the only way to know your getting the most performance.
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"I woke the same, as any other day, you know I should have stayed in bed"
-Soundgarden