First of all, get ALL your paperwork concerning
this seller organized.

If you can access it, save the auction pages to
your hard drive, as Ebay will delete them after 
30 days. If you have the auction #, you can still
leave feedback, even after 30 days.  
Usually what I've done is if I don't get anything 
in 2 weeks, I give neutral feedback asking the
seller to contact me. If no contact in another 
week, I post negative feedback.  

Save ALL your emails related to this deal, 
especially info that includes the other guy's name
and address.

Of course, dig up all reciepts related to your
money order.

Keep as much information as you possibly can and
file it together.  Make hard copies(in other words
PRINT) the emails and other electronic files.

Best wishes sir or ma'am, I hope this works out.