Sounds like you already got wonderful advice. I want to reinforce that from my experience too. I use a HRM to run. I've never had a problem with it falling off as long as it is tight enough. It is really great to gauge how hard you are really working because sometimes I feel like I'm working really hard, but my heart rate is low, and vice versa.
I got really into HRM training after reading a book called Heart Rate Monitor Training for the Complete Idiot. It is really interesting. I've also found the HRM really helpful in interval training.
Good luck.
Kerri