Here I leave you what you need to work with the latest version of Blend fresh out of the oven

.NET Framework 3.0 (Up to 50 MB)

Expression Blend RC (25.5 MB) Requires a Product ID to activate: J33H2-43BTF-JG47Y-KWWWT-43QJV

Visual Studio 2005 Express (Visual Basic or C#) (35-70 MB)

I hope that in a few days our WPF specialists will give their verdict and present us with the abilities and stability of this new Microsoft tool.