If you are using vagrant, you probably-statistically are using git. Make sure you have its binary folder on your path, because that path contains 'ssh.exe'.
Now, modify C:\vagrant\vagrant\embedded\lib\ruby\gems\1.9.1\gems\vagrant-1.0.3\lib\vagrant\ssh.rb to comment out the faulty Windows check and add a real SSH check:
# if Util::Platform.windows?
# raise Errors::SSHUnavailableWindows, :host => ssh_info[:host],
# :port => ssh_info[:port],
# :username => ssh_info[:username],
# :key_path => ssh_info[:private_key_path]
# end
which = Util::Platform.windows? ? "where ssh >NUL 2>&1" : "which ssh >/dev/null 2>&1"
raise Errors::SSHUnavailable if !Kernel.system(which)Now you can do vagrant ssh. Happy camper again!

I'm having no luck with vagrant 1.2.2, any ideas? I've tried both modifying the ssh.rb and altering my path, but to no avail.