This study will evaluate the effectiveness of the drug valaciclovir in preventing transmission of genital herpes from an infected to an uninfected sexual partner. Genital herpes is caused by the herpes simplex virus 2 (HSV-2), or, infrequently herpes simplex virus 1 (HSV-1). Valaciclovir prevents the herpes virus from multiplying and may also reduce its transmission between partners.