Can I file IFR DIRECT with a non-WAAS GPS?
This question was answered here on this Website.  Read the second answer.

Yes you can file direct even without a GPS.  However it would be advisable to perform a RAIM check during your pre-flight along your intended route and determine that you would be in RAIM during the route.  If for some reason your GPS loses RAIM capability then you should proceed using VOR/DME/ADF.  You can still fly direct with using only VORs although that will be more difficult.