To follow up on Greg's post, please see the CLS webpage on Christian Legal Society v. Kane (aka Christian Legal Society v. Newton) for a summary of the case, a copy of the opinion below, and the parties' briefs, as well as other documents.
The Seventh Circuit's opinion in Christian Legal Society v. Walker, 453 F.3d 853 (7th Cir. 2006) (Southern Illinois University) may be downloaded here.
Also of interest: a recent law review article by Joan Howarth, Dean of the Michigan State University College of Law, Teaching Freedom: Exclusionary Rights of Student Groups, 42 U.C. Davis L. Rev. 889 (2009), which discusses CLS v. Walker and CLS v. Kane, as well as related cases. From the abstract:
Progressive, antisubordination values support robust First Amendment protection for high school and university students, including strong rights of expressive association, even when those rights clash with educational institutions’ nondiscrimination policies.