comparing files for changes

Hey guys..
 
i am fairly new to Powershell here and I am trying to write a script that will allow me to "keep an eye" on the file and then write an event in my event log telling me that something was changed to that file.  I really want to base it off of the "write time".  Is there a way to do such a thing? 
I have the commands to create the file and folder, but I just need direction on how to run the looping process. 
 
any help is appreciated..
 
thanks guys!!!

You could run a scheduled task to look at the last modified time of the file then compare that to the last time that the script ran. Usually for this sort of task however I use a WMI Event Sink to make a script fire whenever the file is modified.