I have a 1977 built home in Mn. with oil heat, of which I'd like to add some geothermal
heating and cooling, I have added some solar heat panels which works great.
   My plan is to bury 500 ft. of 1inch PEX. tubing 10ft below ground level in a horizonal loop,
and filling with a R.V. antifreeze, then useing a 1ton heatpump.
   Does this sound workable. Any feedback would be greatly appreciated.

If you're going to go the expense of supplementing with geothermal you ought to go ahead and take a hard look at replacing, not just supplementing. Is 500 ft of loop the max you can get on your property, or is there some other rational for that number? Also, you're going to have a hard time finding a one ton heat pump. The smallest I have seen the specs for is 2 tons, and the incremental cost for additional tonnage isn't that great.

Since you're looking in this direction take a look at the direct exchange heat pumps from ECR Technology or Earth Source Energies. Less in-ground loop and higher efficiency. I plan to use the ECR heat pump in the ICF house I'm getting ready to build.

Tony - there are many things to consider when installing a geothermal heat pump.  #1 - i leave the ground-loop to the professionals.  While it may be "The deeper the better for the ground loop (within reason)", you have to be careful with the diameter of the pipe, the legnth, calculating the amount of glycol antifreeze, and circulator pump sizing.

#2 - I agree with the other user that the size is important.  You want the most out of the geothermal heat pump to ensure that your energy costs remain low.

I recommend contacting a geothermal manufacturer for a contractor recommendation.  Perhaps you can saev on the installation costs by helping with the loop installation or retrofit.  I dont think you could cut costs much on a Dx style system, since the installation is more complex.

Good luck -

I agree, if you are going to install geothermal, go all the way and throw away the boiler. It won't cost you much more and you will save a bundle