Yes, there will be a difference. That's a 1GHz increase in performance right there!!! The C: drive is bigger because it holds 17.6 GB which is much, much, much bigger than 996 MB, more like 17 times bigger.
I think he's referring to just Intel Pentium 4 in general, if a 3GHz will make a difference compared to it's lower 2GHz Pentium 4. But yeah, AMD will smoke an Intel pretty good.