Here is a good article for you. Its written by Terri Warren, one of the leading experts on herpes.
http://blogs.webmd.com/genital-herpes-intimate-conversations/2006/02/type-i-herpes-transmission.html
Aj
You raise a good point - many people are immune to getting HSV-1 genitally because they have already acquired an oral infection during childhood (about 50-60% of the US population!) If you become intimate with a new partner, that person could always test for HSV and see if he already has HSV-1. However, HSV-1 is generally less frequent and severe than HSV-2. Outbreaks and asymptomatic viral shedding do not occur as often. This means that it is less likely that your partner will become infected with HSV-1 than if you had an HSV-2 infection. HSV-1 is transmitted genitally mostly through oral sex. Most people with HSV-1 don't need to take suppressive therapy because they do not have frequent outbreaks (some only have a few during their life), but I suppose if you were having symptoms, Valtrex could help. You should discuss this with a herpes-knowlegeable provider.
Good luck,
Em