OpenRasta is only available in source-code form at the moment.
For these instructions, you will need to install svn 1.5 or later and ilmerge. While OpenRasta runs on plain 2.0, it necessitate version 3.5 of the .net framework to compile, and Visual Studio 2008 for your development.
To download OpenRasta, first do a checkout of the source code. Using the command line:
c:\src> svn co http://svn.caffeine-it.com/openrasta/trunk openrasta
This will download the content of the trunk version in the folder c:\src\openrasta. Navigate to that folder, and build using the provided make.bat script.
c:\src\openrasta> make.bat
This will have generated the OpenRasta dll you will need. All the binaries should now be in the openrasta\bin\release folder.
Based on the version of .net installed on the server you want to deploy OpenRasta on, you can pick between .net 2.0, 3.0 and 3.5. Some functionality is specific to each version