in an interview with the president of the theleton fundation, fernando landeros, he confirmed that kirsten will be there:
—¿Qué habrá en el Auditorio Nacional?
—Se contará con las actuaciones de Alejandro Fernández, Chayanne, Ricardo Arjona, Alejandra Guzmán, Jesse & Joy, Mijares y los internacionales Black Eye Peads y Avril Lavigne. Así como las participaciones especiales de Eva Longoria y la protagonista del Hombre Araña, Kirsten Dunst.
He names the people who is going to perform and the special appereances (kirsten and eva longoria). Yesterday was announced that selena gomez will join them as well.
According to the full article she will be there on friday night when the program starts, then saturday morning she'll be there answering phones till 10 am and then, on sunday kirsten and longoria will give a press conference to talk about the project and how was their experience there. They'll spend saturday afternoon with the people from CRIT helping them in their support center.
CRIT is a rehab center for children sponsored by the theleton
Part of the theleton will be aired in the US by galavision (tv) and univision radio. If not, univision (tv) will have some info, images, clips and interviews from the entire weekend on monday in their morning shows and then en "el gordo y la flaca" in the afternoon.
this is the official web site of the event:
http://www.teleton.org.mx/ 
update: The theleton w/s just uploaded this with some of the stars that will be helping and kirsten is indeedincluded:
http://teleton.org.mx/index2.php?option=novedades&task=view&id=245&pop=1&page=0update 2: univision.com will also air the theleton starting tomorrow night at 11pm/ 10C