For those of you, who like me, can't upgrade to IE7+ due to corporate restrictions, you can still install Fences.
Go to http://www.impulsedriven.com and install the latest release of Impulse. It will complain that you should run IE7+ but will allow you to complete the install.
Once Impusle is installed, you can go to the My Software tab and you should see Fences in the list. Install/Update from there.
If you really don't like/want Impulse, you can then uninstall it from your machine without impacting Fences but you will need to go through this procedure again when Fences 1.0 is released.
While I don't particularly like getting saddled with another auto-updater app manager (like Apple, Adobe and several others force on us), having the option to remove it after the fact is very nice if installed this way.
-Robert