I'm at NP for a few years and never thought about it. Now that you asked, I just checked it and it appears you can.
1. go to the designs contests main directory here: Design Contests - NamePros.com
2. on the right side click "forum tools" and then
3. click "subscribe to this forum"
4. and chose "daily updates by email".
By the way, if you want to keep track of all the threads you have ever posted in, make the following link a bookmark. If there is a new message in that thread you will see it in the list. http://www.namepros.com/usercp.php