The problem is that AMD followed Intel in naming, but their processors don't have the speed of the Intel chips. So your AMD 3000+ is an equivalent of a Pentium 3.0. That's why the salesman said it's a 3 GHz chip, although its nominal speed is not 3 GHz. The problem with a motherboard upgrade is that you'll probably need to buy new memory as well. That is, check the specs of your old M/B and see what kind of memory is there and then see what your new M/B takes. XP 3000 is not that new, and you shouldn't have problems with using the old memory, but check nevertheless.

-- erlik