On a slightly different topic does anyone know what minimum level of equipment is needed in an aircraft do an IMC?
If you mean to train, then the answer is ADF, DME, VOR and ILS.
To use the privileges of the rating you need an ILS to do an instrument approach(fairly obviously); if you are in controlled airspace you must have all the above, and they must be FM immune. This means that outside of class D you can fly IFR and do instrument approaches using non FM immune kit. To fly IFR outside controlled airspace you do not need ADF/DME etc but it would be sensible to have it. You must carry Turn and Slip, AI. DI, VSI, Altimeter and a clock with second hand.