I agree compound is more effective than isolation moves but I still think if you are a newbie just go with whatever you have on hand and if that's 2 lbs, so be it. Just make the best of it and be prepared to increase the weight as you progress. Just a couple of cans would be 1-2 lbs depending on the size and most people have some cans in the kitchen.
If you want to ballpark starting weights for varying things, the best beginner chart thing I ever read was in Anja Langer and Bill Reynold's "Body Flex, Body Magic." While not spot on for me in all things, it was quite close. It expressed the starting weight as a percentage of your body weight and that's what I liked. I never saw it that way anywhere else.
The only trouble it is for gym style workouts, so if you are working out at home to a DVD with dumbbells, it isn't exactly going to match and you have to consider the DVD's routine. Some are too fast to be changing weights for each thing.
But anyway I took a pix of that page in the book:
Note this is an older book -- and lat pulldowns behind the neck aren't the way to go. Do them in front.
HTH!
A.