Hey Dario, I agree with what most have mentioned here. Get a dedicated server with some type of DDOS protection, become a microsoft partner, and get a SPLA agreement.
Just beware that the pricing on Windows licensing is supposed to be increasing. Instead of a per-processor pricing structure, which is what they're using now, they're going to be changing over to a per-core pricing structure. I never found out if they were going to apply this to their older Win 2008 versions too, but you may want to find out before hand.
If you speak with the guys over at Insight, they can help you get started with all of the paperwork for joining their SPLA agreement. You can then either activate/use the dedicted server editions of the license (which allows unlimited windows vms, 1 license PER processor but again may change or have already changed to a per-core structure) or just get individual licenses which is much more expensive. Good luck