I believe CFL's are self ballasted, anyhow they just plug straight into a regular socket, you don't need anything else. You need a ballast for a HID (both MH and HPS), ballasts are matched to the bulb that will be used with it, so you can't use a 400w bulb with a 250w ballast etc.

When looking for CFL's you can find them in 2 basic colours, white, spectrum around 6500k (normailly marked daylight on the box) which give out a bright white light, these are best for veg. The others are more yellow in colour, spectrum around 3000k and will be will be called something like warm white, this is similar to the evening sun and are more suited to flowering.