a couple of things to add. Like bob said, for your first couple of workouts you can slow your rep speed down so the set is still difficult
when you get closer to your rep max than you may only be able to do 1 set instead of two. by the 5th workout on 15's i will not come close to 2sets and will only do 1.
as for estimates. This is what i do. I get my 15 rep max and base all other workouts from that. This might not work for others. I have always been better at higher reps. since i was a kid i lifted at 10 reps so I was never as good at lower reps
say my w/o 15 rep max for bench is 250. I will do 1 set at this weight.
next workout i start 10's. I will start at 240x2,250x2,260x2,270x2,280x1 or 2, 290x1 or 2. If the 250 was very difficult you may need to do 240 for your first two w/os of the next rep scheme. hsthsn.com has many q's like this answered for ya.
as for chest i do 3 sets. 2setsbench and 1 set incline db day 1, day 2 i will do 1 set bench 2 sets incl db. same with back. this is what i do. There are many little variations but like bob said, stick to the program w/o changes for a time or two. than start tailoring it to fit you better.
lots of info on this at
www.hsnhst.com