Basically, the 3000+ is a performance rating, it does roughly equal a Pentium 4 at 3GHz.
Of the two I'd pick the Athlon even though it's older, Pentium 4s put out too much heat for my liking. With it being an Athlon XP as opposed to Athlon 64 (which is what I thought when I read this the first time) the Athlon may be slower than a P4 at 3GHz, but it's by no means a bad processor.
Not sure what he meant by "Clock down" here though.