Interestingly I have an AthlonXP machine at home (+2200 768mb of PC2700 RAM, 80gig 7200rpm HDD, ATi Radeon 9000PRO 256mb, DVD+-RW) and a celeron machine at work (2.6GHz, 1gig of PC3200 RAM, 80gig 720rpm HDD, ATi Radeon 7000 series 64mb, CD-ROM).
It's not a fair comparison really as has been pointed out earlier in the thread. Without benchmarking I would say that both are very similar in General Windows use. I notice that the Celeron slows when several application are open and that the Athlon only stresses when I'm running Access queries and iTunes along with all of the usual office and internet stuff. Obviously the Athlon wins on the Games front as well.
I've replaced the motherboard on the Athlon and Socket A boards are getting thin on the ground. Add that to the hassle of getting Microsoft to believe that you aren't moving XP onto a new PC and I'd be tempted to go for the Celeron. I used to be a processor snob but I'm quite happy with my work machine. Add some more RAM and application hangs get less and less.
Hope this helps.
BigK