1) Install GeekTool
2) Run this script....
#!/bin/bash
USERNAME="[email protected]"
PASSWORD="password"
EMAIL=`curl -u $USERNAME:$PASSWORD --silent "https://mail.google.com/mail/feed/atom" | tr -d '\n' | awk -F '<entry>' '{for (i=2; i<=NF; i++) {print $i}}' | sed -n "s/<title>\(.*\)<\/title.*name>\(.*\)<\/name>.*/\2 ... 