I have a dual P-III in my office... used to be the studio machine back in 97 or 98. If you are running older software and it is capable of using 2 processors, you'll get some benefit. Most older stuff is useable, so long as we have realistic expectations.
Sorry, I don't know jack about softsynths.
"I believe that entertainment can aspire to be art, and can become art, but if you set out to make art you're an idiot."
Show business: we're all here because we're not all there.