Well, well, well, the world of VST. I use VST's. They are created by steinberg but are cross platform. I use VSt's in Fruity Loops and Cubase SX. There are some very good companies that continue to deliver great VST's for instance, Native Instruments, or Waldorf. Native Instrumens account for most of my VST's. Kontakt for sampling, Pro-53, Absynth, FM7. With these I have a large amount of instrumetns with the capability to use EMU and Akai Cd's. I use Fruity Loops as a VST also inside of Cubase for drums sometimes and Native Instruments Battery to play chopped loops.
I will say that for a serious user either use a dedicated PC for VST utilizing VST System Link in Cubase SX or if unable a fast processor with 1 gigabyte or more of Ram, Because they eat up system resources.
Do research, go to Steinbergs website or my favorite Tweakheadz.com. or pick up Home Recording or another mag that features soft synths.
I save money because I can buy a midi controller and have a gang of sounds at my disposal instead of Racks of synths and a expensive keyboard. Which I wouldnt mind don't get me wrong.
Thelonius