Everything plays a role in FS9.

Think about it the data has to be free flowing all the time form any component in your system.  Get a hold up anywhere and you will get a stutter.  The system has to work together to achieve its best.

If you were to overclock then it means your system would run faster and move data quicker, though I would not worry about playing with this yet.  Just get your system setup and maybe tweak it but no serious overclocking.

1gig of ram is ideal for FS9 and XP operating system.  You will however still find it uses a bit of your page file but dont worry thats normal. 

How do I explain the HDD thing.  OK this is how it was explained to me.  You have a filing cabinet and its got a few files in it, this makes it easy to find stuff.  Once it gets more full it gets harder/slower.  Now if you had an even bigger filing cabinet but with the few files in it you have a smaller area to search still so its faster, get it??  Think thats how it was explined to me.

Sata drives also have a faster seek time so you shold find data transfer and loading times become faster too.

Once you get up and running with XP let us know and we will maybe try a few things.  I do remember on my mobo somthing to do with my ram in BIOS.  It cam set at 2T and I set it to 1T this improves things a bit, but yours may have come set at 1T (Means the ram works faster)