I have a little experience of this.
1: The advertised rating of an Athlon chip isn't an actual clock speed, it's the claimed equivalent speed, based I think on a Pentium. Because of such things as a more efficient internal organisation, this means that one Athlon clock cycle does more work than one reference-chip clock cycle. There was some initial scepticism about this, but AMD seem to be staying honest. 2: There can be more than one way of getting the correct speed, and motherboard settings can sometimes allow different combinations of clock speed and CPU-multiplier. I had some trouble with this on mine, until I found that I was getting the quoted speed by overclocking the PCI bus. Changing a BIOS setting allowed the PCI to run at the correct speed, while still giving the correct clock speed to the processor. 3: Modern motherboards should reliably auto-detect the CPU, rather than needing jumpers changing and BIOS fiddling, but check the defaults and the manufacturer's web-site. Mine came with a CD of drivers, and a movie of a rather cute Chinese lady showing which part went in which hole...