TOPIC: Under construction page

Is there a way to have the site show an under construction message, but also have a link to my other site until I get the the new site completed?

No one will be finding this site for at least a month if not longer. It's going to take time for Google to move you up the rankings to the first few pages where you will be seen. If you put the site in maintenance mode you slow down your ranking increase as Google has nothing to scan.