While I have since upgraded my system to Pro Tools LE and no longer run this plug-in or Cubase SX, when I did I ran it on a Hewlett Packard lap top that had a 3.0 Ghz processor and 2 GB of RAM. While I didn't use this plug-in everyday, when I did I never had any problems at all running it. I would really only run one at a time and I believe that most will be doing the same, but I can't say how well it would run if you wanted to run a lot of them at once, but I'm not sure why anyone would want to do that anyway.
I've been using the Steinberg VB-1 Virtual Bassist plug-in for about four or five years and while I no longer have the proper software to run it with, it definitely served me well when I was using it. Since it came with Cubase SX for me, the price was virtually free and I know it is pretty cheap even if you buy it on the side. The sounds on the Steinberg VB-1 Virtual Bassist plug-in are pretty good and work great when you want to put down a MIDI based bass track. If you are looking for a nice and easy to use plug-in that will give you a wide array of different bass guitar sounds, the Steinberg VB-1 is worth a try.