Becki, depending on which direction you are approaching from, just before the Pell (Newport) bridge, or just after it if you are coming from Newport, take the exit for Downtown Jamestown.
You will be on Conanicus Avenue. Follow this through the small downtown area (there is a parking area there where you catch the ferry to Rose Island in-season and a distant view of Rose Island) and up the hill and turn right onto Hamilton Avenue. This road turns into Beavertail road at the stop sign. Continue straight (more or less) onto Beavertail Road, across the strip of land which connects the 2 islands of Jamestown and follow the road for about 2 1/2 miles which will bring you into Beavertail Park. Continue around the lighthouse and there is parking there.
Jim
Johnson