Celeron or Duron and P3 or Athlon T-Bird

Celeron and Duron are great consumer chips, both are cheap, work very well and run at comperable speeds. P3 and the T-Bird are wonderful gaming chips, probably made for bigger apps. I wonder if all the extra power is actually needed to run apps like Office XP or even Windows XP. I have already considered buying a Duron Computer and then later upgrading the chip to a T-Bird. If anyone has any insight on the chips listed above (benchmarks would help) that would be most helpful. Thanks