Good question
And I'm not sure I'm qualified to answer, but I'd think that if you pick up a dumbbell at the store and can (bicep) curl it 10 times and get a nice burn (but not be completely exhausted) it would be a good start (and maybe a tad heavy given that most times you'll do 3 sets and that third set will be really tough). Then you'd want to go with one pair of dumbbells heavier than that and two sets less than that. That would give you what you need for shoulder chest and back work. Then you'd gradually work your way heavier, buying pairs slowly. Or if you have the money available, go with one of the Nautilus adjustable dumbbells (where you dial the weight and it goes up to over 50 lbs per dumbbell. Ultimately it would be cheaper if you keep working heavy, but it is a BIG investment. I've got a bit of dumbbell envy over them actually at the moment.
I had worked doing Turbo Jam and some Firm workouts with 3s, 5s and 8s, and I now have dumbbells up to 20 lbs (12,15,20) plus some dumbbells that use plate weights so that I can take it up to 30 for some back work.
One suggestion for when you buy your barbell... make sure you don't buy threaded and instead get a sturdy bar with quick clips. It will make your workouts much more enjoyable. I have a great threaded bar (13 lbs heavy) but switching weights is VERY cumbersome and clips don't work on it. Eventually I'll invest in another bar and that one will use clips!
Shani
