Actually these are dead easy on the focus. They are (usually) part of the drum. Get premium drums with the wheel bearing attached, use a 29mm bolt to get the existing drums off, REPLACE THE NUT with a new ford-spec nut (about $6, worth it!), tighten the nut (and new drum) to 175 lb-ft, and you are good to go.
Wheel bearings are not for the beginners or the squeamish. They are contained behind the brake assembly in a container filled with heavy goop lubricant. When the bearings wear out they whine. They need to be replaced by a mechanic experienced with it. If it is done wrong you stand the risk of losing your braking functions.