I am no longer running Steinberg Halion as I no longer use Cubase SX, but when I did I ran it on a Hewlett Packard lap top with a 3.0 Ghz processor and 2 GB of RAM. The only reason I no longer use it is because I have switched to Pro Tools and this isn't a compatible piece of software with Pro Tools. While I was running this in Cubase I was able to run it quite well without any processing power problems. As long as you have a decent system I think you'll be okay with running this software.
I first used Steinberg Halion about four or five years ago as it was one of the first virtual orchestras that I used and used it a lot as I was always impressed with the sounds. While they aren't the most realistic looking back, they do get the job done if you want to get some orchestra sound in your songs at a cheap price. It is versatile software which definitely adds to the reasons that this is a good piece of software. The price is reasonable, but I would probably recommend looking into the newer versions of this software as it probably sounds better and is more up to date...