About the SATA harddrive. Yes they are better harddrives, but don't they perform just as well as EIDE drives unless they are installed in pairs? I believe there are no operating systems that support their extra speed and enhanced performance, therefore it would be cheaper just to go with an EIDE drive. But if you do feel it's worthwhile for the extra speed, then perhaps you would consider dual drives.
As for the processor, definitely go with a Pentium 4. Athlon 64s are superior when it comes to gaming and accessing webpages, however, Pentiums handle nearly any type of multitasking much better. Everything else sounds good.