Fruity loops!
hehe sorry gotta laugh. [:D]
The VSL samples are vast and huge and really you need either the Gigastudio, Kontact player, EXS 24 mkII, or Halion to run them. There isn't just a few different wave files for each sound, there are hundreds. Each note is independantly sampled.
Your P4 could run several instruments with 1 GB of Ram but you really would need Cubase or Digital Performer running Kontact or Halion otherwise your gonna be stuck. And lets face it .. if you have the money to buy the VSL I'm sure you can buy Cubase (even a second hand version on ebay).
Otherwise I really don't think Fruity Loops is gonna cut it. Don't get me wrong it's a fun program, but that really is not enough to drive the VSL.