I don't have time to research everything here.
I would by the fastest clocking Intel Core Duo chip you can afford. You can upgrade Ram cheap later but the CPU is more $.
I have heard arguments about paying more for better manufactured RAM. I go with the dirt cheap sale that I can find at Fry's or Compusa or where ever I can find my RAM type dirt cheap. I run Calkwalk DAW with 4 gig on XP sp3 and cheap ram is fine.
A more expensive CPU may have more instructions or higher cache or better cooling. You don't need any of that. Just buy an Intel Core Duo and you will be happy. BTW with cheaper CPU's you loose the same thing, instructions or cache or cooling.
Go SATA with your HDs
RAM speeds only factor into apps like CAD or lots of Audio/video production. I would say having more RAM is better than having less RAM even if it is faster. Once you start paging to disk your speed increase is voided.
Always install Ram in pairs, more paths on the board means less choke points. Stay cheap but max it out IN PAIRS.
Let me know if you need more info.
Install RAM in pairs
Buy cheapest,fastest ram you can find for your board, cheap trumps fast
Go Intel Core Duo if compatible with your board
SATA HD's I always by a boot disk around 80 gig then a Data disk of 500+gig
RUN XP - INSTALL XP SP3!!!!! and all patches before install your apps.