You would need to use two separate sprite batches for each type of drawing. One for the blocky. One for the blurry.
Use this overloaded method when you begin your sprite batch:
SpriteBatch.Begin (SpriteSortMode, BlendState, SamplerState, DepthStencilState, RasterizerState, Effect)
The result should look something like this:
SpriteBatch.Begin (SpriteSortMode.Deferred, nil, SamplerState.PointWrap, nil, nil, nil);
//SpriteBatch.Draw(**blocky stuff**);
SpriteBatch.End ();
SpriteBatch.Begin (SpriteSortMode.Deferred, nil, SamplerState.LinearWrap, nil, nil, nil);
//SpriteBatch.Draw(**blurry stuff**);
SpriteBatch.End ();