Most HR departments assign a person to support the law department. That person may also support other functional areas, such as finance and information technology. For a law department, the HR rep typically carries out a number of tasks.
They provide comparative compensation data (See my posts on March 26, 2005 about executive search firms possibly inflating compensation and June 15, 2005 on compensation in Asian law departments.) They prod people to complete the annual evaluations of lawyers and staff (See my post on May 4, 2005 decrying forced rankings.) Often, the HR person helps in decisions about promotions, which include setting titles and compensation levels.
The more ambitious representatives will also contribute in terms of ongoing, professional training. (See my post of Nov.6, 2005 on continuing legal/business education.) And even further afield they can assist on teamwork development in the department (See my posts of 2005: Oct. 1 on the Johari window, April 9 (Hartman-Kinsel), April 18 (MBTI), Oct. 19 (MLE4), and Oct. 21 (MBTI as amusement.).