How complex is the model? The RAM may be a limiting factor. I notice you have 512MB on both machines.
I hate to say it, but it is also possible that the Athlon is better than you think. Intel has been pumping up the Pentium line's clockspeeds more for marketing than actual performance. Competitors' chips have typically outperformed Intel products at the same MHz/GHz rating. It is interesting to note, now that the Pentium line is reaching its limits and the Itanium's present top of the line is 1.4GHz (with 1.6 and 1.7 announced), Intel has decided to stop marketing on clockspeed. Instead they will be marketing their processors as 3, 5, and 7 series (sounds familiar to BMW owners eh?
).
If IBM can keep to their roadmap with POWER series chips hitting 6GHz to 10GHz over the next few years we may see a curious reversal with Intel picking up Apple's old Megahertz myth ad campaign.