Behind The Name and Namepedia are some free Web translation services that let you to translate names between multiple languages -- among them English and Spanish. Many traditional English names have direct Spanish equivalents.
Many given names in Indo-European languages have common origins and can be translated directly from one language to another, particularly those that come from the Bible or from the names of saints. Some examples are Mary - Maria, George - Jorge, Mathew - Mateo and John - Juan. Some names are written identically, such as Martin, though the pronunciation differs.
Sometimes, the names have diverged quite a lot from their common origins and no longer resemble each other very much. The Nordic name Lars, for example, translates as Lorenzo in Spanish.
Not every name has a direct translation. Wolf would be "lobo" in Spanish, but that is not a name. Names from languages outside the Indo-European family often have no equivalent. Surnames generally are more difficult to translate, as naming conventions differ. Patronyms such as Anderson and Johnson, for example, are not used in Spain or Latin America. For some surnames, there are direct translations that are also names, such as the case with Smith - Herrero.