How should I publicize a university event of wide interest?
Not sure which of these things you already tried, but here goes (note you don't have to do all of these -- I'm just brainstorming here):


create flyer (letter sized)
create poster (not sure of exact dimensions -- I think it's about 11 x 17, somewhat glossy)
ask the people on the list you were given to put up copies of your flyer (attached to your email)
put flyers and posters up on bulletin boards and in elevators
involve students in your publicity efforts
get an article in your campus newspaper and your town or city newspaper, in advance of the event
do direct outreach to target relevant sectors of the community
liaise with relevant student organizations
plan to serve refreshments, and mention them in your flyer and poster
arrange a back-up larger venue in case your publicity efforts have too good an effect