Can AnkhSVN be installed on an Express edition of Visual Studio?
No, because the Express editions explicitly do not allow plugins. See also AnkhSVN's FAQ:
Does it work with the Visual Studio 2005 / 2008 / 2010 Express versions?
No, and it might never do so. The current position from Microsoft is that these SKUs will not support addins.
That being said, there's nothing stopping you from using any other source control tool outside of Visual Studio. It's really not that painful to drop back to a command line for a commit.