I just came across an interesting item:
http://www.e-dealsusa.com/1359.htm
This is good news since it would mean that if Interplay goes under (completely), there will be at least one other outlet for D3 for Windows. I checked the Sold Out Software site, but they don't list this item (yet).
Be aware that Sold Out has had a standing deal for some time where you can get three titles for the price of two. This equates to almost free shipping to the U.S. on three games for a total of about $30.00 US.