It all depend on your VST host as well. Cubase and Nuendo will only work as a master and not slave to the MPC. Other sequening software (I forget which ones) will allow the MPC to be a master.
If you only want to run your VST instruments without using a sequencing software, I'd recommend VSTack or Chainer. There's another similar VST host that's actually freeware, but I don't remember the name. You might be able to find it by searching the fourms (since that's where I read about the freeware), or try Google.