Foscarnet is a drug that inhibits viruses and has been shown to be effective against infection with Cytomegalovirus and also against infection with the Herpes simplex virus in several patients with AIDS. Vidarabine has been shown to have activity against the Herpes simplex virus in patients who do not have AIDS, but it has not been studied in patients who do have AIDS. This study compares foscarnet and vidarabine treatments for AIDS patients who have herpes simplex infection that has not responded to therapy with acyclovir in the hope that one of these two drugs will help to stop further progression of the herpes simplex infection and may have fewer side effects.