I just noticed that Paul Andrew blogged about the latest release of Windows Workflow Foundation. There are some important caveats to installing this release so please review the important notes section on the download page.
The download page is a little confusing. Even though it says Visual Studio 2005 Extensions for Windows Workflow Foundation Beta 2.2, it actually contains the Windows Workflow runtime and SDK as well as the VS add-ins.
In other words, it contains everything you need to use the latest version of Windows Workflow Foundation. As Marc points out, however, there is an important caveat. This version is not compatible with the WinFX February CTP, so you need to uninstall it first.