Yes, you can spray your vinyl siding. I don't know why anyone would but since yours has been painted already, you will have to keep it up every 5 to 10 years.
For preperation just power spray it with a detergent and rinse. CAUTION do not get too close or too high on the pressure, it can penetrate the siding.
Any good latex or vinyl exterior paint will cover it just fine. I have used 100s of gallons of Wal-Mart paint with no problems at all.