Here's the agenda for the 2012 Pittsburgh Marathon, which takes place on Sunday.
The marathon weekend begins on Friday (11:00-8:00) and Saturday (9:00-6:00), when there will be a Health and Fitness Expo at the Convention Center. Also on Saturday, UPMC Sports Medicine and UPMC Health Plan will host a 5K run at 8:00 a.m. At 10:00 on Saturday, there will be a "Kids Marathon" (actually a one-mile run).
On Sunday, the marathon will start both for runners and walkers at 7:30 a.m., with the wheelchair division starting at 7:20. A marathon relay will also begin at 7:30.
You can find a course map here. The starting point for the marathon is downtown. From there, it winds through the Strip District, North Side and South Side before heading east to Oakland, then to East Liberty, Bloomfield, and back through the Strip District before ending up back downtown. Here is a list of fluid stations and aid stations. If you're planning on driving Sunday morning or early afternoon, here is a list of roads that will be closed.