As previous tips have mentioned, the campus newspaper provides a great mechanism for getting your organization's message to the student population. But don't forget that there are other media outlets serving your campus and community, notably local newspapers, television news networks, and public access stations. Invite these news outlets to your events, and try to build relationships with their staff to help get your message out.
The first step is to craft a press release for your event. This should include the event, speakers, sponsors (the more you have, the more likely you will be to get the press interested!), location, and time, as well as contact information for your organization. Send this out to local media at least a week ahead of time; fax numbers and email addresses will be available on the appropriate websites.
Next, craft a media packet with information on the issue being discussed at your event. Don't get polemical -- include hard facts and statistics, and make sure to cite sources. Make sure to reiterate the information in your press release, as well, including biographies of speakers, the mission statement of your organization, and your contact information. This will make it easier for a reporter to cover your event, and thus increase the likelihood of getting space on the page or in the evening news.
Remember that colleges serve as a source of pride and identity for a community: local inhabitants want to know what students are doing! So don't be shy; contact your media, build relationships with reporters, and spread your message!