My first century is in 6 weeks and here's my rough plan for long rides, increasing mileage 10% each week...

week #1 (next week) 57miles
week #2 63 miles
week #3 70 miles
week #4 77 miles
week #5 start tapering down mileage
week #6 Cool Breeze

We did 51.9 miles today and in addition to one long ride each week I plan to get in two or three 25-35 mile rides and maybe a couple of Spinning classes each week. I also lift weights at the gym, but I think I will cut back the intensity of my leg workout so I'm not sore.