Non-mormons can tour and visit the temple during the openhouse before it is blessed/dedicated. Once it is dedicated then only worthy members of the LDS church may enter. Just so you know not all members of the church may enter the temple after it is dedicated. Only those that qualify by getting a temple recommend can enter the temple. 
 
Before temples are dedicated they have an open house for several weeks. For example, there is a brand new temple in Vancouver, Canada that is having an open house during April 2010. Here's some info about it: Vancouver, BC Temple Open House 
 
 
Here is a good place to get some info and get other questions answered. LDS Temples - FAQ