Windosr-Tikal worth the effort? Would be like going to Eygpt and not visiting the pyramids. Real easy from San Pedro, Maya Island offer good packages with everything.
Spooky-Just a few rental agencies allow you to cross the border with a rental vehicle, but they can;t insure your car. So...Plenty of ways to get there and back. The SI Hotel can arrange it for you or steeer you in the right direction. I like the Jungle Lodge in the park, the plush Camino Real about 35 mins from the park and also like the smal hotels on the island village of flores,and get a taste of Guatemala.