I'm no longer running the Steinberg Embracer virtual instrument since I no longer run Cubase, but when I did I ran it in Cubase SX 2.0 on a Hewlett Packard dv8000 lap top computer with a MOTU 896 HD audio interface. The computer had a 3.0 Ghz processor and 2 GB of RAM. I can't say that I remember ever having a problem running Embracer within this configuration, although I definitely never had a need to run more than one instance at a time. It's hard to determine how well a certain piece of software will run within a certain configuration without actually trying it, but I don't believe that Steinberg's Embracer is the type of software that will take up too much of your processing power.
Overall, Steinberg Embracer is a decent virtual instrument at best. The sounds are mostly strange and and atmospheric, but there is indeed a lot of room to play around. While versatile, I just wasn't impressed with the overall tone quality of this virtual instrument. It is definitely worth noting that this is a rather old piece of software and could be considered outdated at this point. I no longer use this in any capacity since it isn't compatible with Pro Tools, and even if it was I probably still wouldn't use it. If you're running Cubase or another Steinberg manufactured sequencer, I'd recommend checking it out as there are a few cool things that you can do with it, but overall this is definitley at the bottom of the list when it comes to virtual instruments in my opinion.