compare information

I have a Machines.TXT file that has 1 machine per line.   I need to find out if any of the systems in Machines.txt are in a specific OU within AD.  I can get all of the machines from my target OU and then use Beyond Compare but I wanted a pure PS solution.  Now, I have code that will read the machines.txt and then do an IF statement against it but how do I compare what is in machines.txt to what I find in the OU?    I'm not sure how to structure this.   Ideally I'd like to write to a new file all of the machines found in the AD OU.