Are your samples playing back sluggishly? Like they need vitamins maybe or a little Geritol? Putting all your various computer-based samples and virtual instruments on a separate hard drive (FireWire or USB 2.0 running at least 7,200 rpm) from your system or boot-up drive will definitely improve performance, regardless of whether you are playing them in a live performance or as parts within a multitrack recording. This is also safer in case you have a major system crash and then end up having to track down all the original discs to reinstall everything. Often installers will by default place your samples on your system drive, in which case you will need to move them and then the next time you fire up a particular software instrument, you will likely have to tell it where the raw samples are stored.