they look to me like very small mealy bugs, scale, or possibly very opaque aphids. (See if you can get a positive I.D. by looking up pictures, since you can see the critters better then I can.)
Use some kind of non-metal based insecticide on them, if the plants are to delicate to just pick the bugs off of. Metal based pesticides will harm you plants.
Likewise, never use any soap based product.
One popular option is Neem oil, although I use a sulfur based Safers brand solution.
The Savage Garden suggests the following insecticides, if you have them or can get them at nearby stores: Diazinon, Malathion, Orthene, or wettable powder Sevin.