Well, if the chrome is in good shape then it takes some doing to paint over it and have it stay. My favorite way is to use weak battery acid. Think my last mix was 75% H2O to 25% acid.
First clean the chrome real well using dish soap. This will strip any wax and such. Rinse with cold water. Dry. Brush the acid all over the chrome, let it soak for approximately 15 minutes. Rinse with cold water. Repeat. Dry the chrome, wipe it down with your favorite pre-paint treatment and a tack free cloth. Primer. Paint. Light multiple coats until it looks good.
Alternative method is to use 3M green scrubbies to scuff the chrome and paint. Lots more work intensive tho. And I've had this method fail on me. The paint began flaking off within about 4 months. No rust on the chrome underneath tho.
Sarge