Yes, but it will not be as bright. You may not want to change the bulbs if they give you light for doing makeup in the mirror. You might be very dissapointed in the quality of light the CFL's give off. While CFL's save electricity, they still require mercury in order to be produced which is a non-replenishable resource. So while everyone is doing their part to save electricity, they are really just ridding our planet of a useful resource. Turning off lights and appliances, and not running an AC would be much more effective.
I believe you can.
The old 100 watt light bulbs were pretty good, giving enough light where you need it. The new light bulbs (CFL) are definately not as bright and I am really disappointed in them.
I stocked up on some of the old bulbs before the new ones took over the world so I'm still wasting energy but much happier.
You can always go smaller in wattage. Fixtures will typically have a limitation (like 60W) that is due to heat issues. That means REAL watts, like if you have an incadescent bulb. Your 60 watt CFL isn't 60 watts, but rather 13 watts. They just call it that because it is about the same brightness of the incandescent 60 watter. My wife in her plant room put in 75 watt (approx 300W equivalent) CFL's in her 75 watt fixtures for the plants.