I installed a brand new copy of Windows 7 Enterprise Edition (64 bit) and Visual Studio Premium. I installed Visual Assist 1819 but it doesn't show up in the IDE nor does it work - it is like it's not even installed. It doesn't appear in the Extension Manager either.
Did the Visual Studio 2010 version selector appear when you ran the .vsix?
Are you using VS2010 RTM?
If you are running Visual Studio 2010 with administrative privileges, are extensions allowed to run: Tools | Options | Environment | Extension Manager | "Load per user extensions when running as administrator"