Untar the attached file somewhere, then:
1: chmod 644 /path/to/gsi_keys/hostcert.pem
1: chmod 600 /path/to/gsi_keys/hostkey.pem /path/to/gsi_keys/hostproxycert

Now to setup the HTCondor daemons:
1: in condor_config set GSI_DAEMON_DIRECTORY = /path/to/gsi_keys
2: in condor_config set GRIDMAP = /path/to/gsi_keys/mapfiles/grid-mapfile
3: in condor_config set SEC_DEFAULT_AUTHENTICATION = REQUIRED
4: in condor_config set SEC_DEFAULT_AUTHENTICATION_METHODS = GSI
5: For HTCondor 7.9.x and later in condor_config set GSI_SKIP_HOST_CHECK=true
and that should do it on the HTCondor daemon side of things.

Optionally, edit =/path/to/gsi_keys/mapfiles/grid-mapfile= and replace =USERNAME_HERE= with your username. This is not necessary to get the daemons to start up, but needed for condor_submit.

On the client side, for simple testing without the need for grid-proxy-init and friends, you could just set the following environment variable for the tools to use:

   setenv X509_USER_PROXY /path/to/gsi_keys/hostproxycert