While a PM might be great, there's no reason that you can't train well and get results without one. Dave has given you some great guidelines, and there is plenty of info on this forum and around the net on SST. Training itself will give you plenty of feedback of where you should be working, as will your HR/speedo/timer etc., not to mention PE.
FWIW, I ride with a variety of groups, and in plenty of events with LOTS of riders from beginners to elite, and I've yet to even see a PM in use ... and still plenty of those riders go very very fast!
Enjoy.
B