I have a Windows based computer that is a Dell, and it has a dual core processor. For sound card I have a MOTU firewire card, and I use it with the Nuendo host. This expansion works perfectly with my system. The CPU load is relatively light compared to other drum programs, but you can expect to have a heavy hit on your ram, which is about 300MB of samples with the default setup loaded. It is very stable, it has not crashed that I have seen.
I have had this for nearly a year I believe. The best thing about this is the really odd sounds they give you. Things like hitting a desk drawer, zipping up a jacket, and hitting a pan. These are sounds that can really give your song a unique touch that you probably wouldn't otherwise think of. On the other side of the coin though, the fact that these sounds are so weird definitely limits their usefulness, so I have ended up rarely using this expansion. I will say that when it has been used though, it has been great. So overall I feel that this expansion is not really necessary for your ezDrummer collection unless you have some extra money and you want to have a luxury. It is not the greatest value, but it is nice to have for that odd song that needs something different. I would probably not get it again.