我可以在客户端计算机上获得什么最低版本的.NET？

I know that in general I can expect .NET 2.0 or better installed on most client/customer machines since it's been included in Windows XP SP1 (SP2?) for some time and comes standard in Vista/2003/2008. But my question now is, can I expect .NET 3.0 to support WCF/WPF? We build component libraries so we can't make too many assumptions and requiring that the our development customers include the 3.0 installer is not ideal. I know that in general I can expect .NET 2.0 or