If you're in the area and want to do something, go to public events and ask those who support his visit to denounce his past statements and actions, then upload their responses to video sharing sites. Don't bother with rants, emotional or otherwise, and don't bother asking Bustamante something unless it's good. Concentrate on local officials or those who work for local groups. Kent Willis of the Virginia American Civil Liberties Union is quoted in the article, but his position on the visit isn't clear (although it can be assumed).
UPDATE: Here's video of a Lou Dobbs report on the visit: link.
A United Nations human rights official has postponed a planned visit to inspect the treatment of immigrant workers in Prince William County, according to the activist group Mexicans Without Borders. The group had welcomed the outside scrutiny, saying the county's illegal-immigration policies have "created a climate where suspicion and terror thrive."
Jorge A. Bustamante, a U.N. special rapporteur for human rights of migrants, called off a visit planned for yesterday and today. In a letter to Mexicans Without Borders, Bustamante cited "something unexpected of extreme gravity" that was "totally outside of my control" as a reason and did not indicate when he would reschedule the trip.