This site is no longer a place from which to download Cog VMs.  Cog source code has moved from the squeakvm.org subversion repository to https://github.com/OpenSmalltalk/opensmalltalk-vm from which VMs are built automatically on https://travis-ci.org/OpenSmalltalk/opensmalltalk-vm with the products available from https://bintray.com/opensmalltalk/vm/cog.  To access a build, visit the bintray link, select a version number in the “versions” column and then click the “Files” link.
You can find old unofficial pre-built VMs for both V3 and Spur format Squeak and Newspeak images under http://www.mirandabanda.org/files/Cog/VM/.
You can find old bootstrapped Spur images in http://www.mirandabanda.org/files/Cog/SpurImages/