Here's a dirty script I wrote to install nagios and Lilac on a clean CentOS 5.4 install. This script doesn't care about anyone other than itself (it'll change the mysql password for instance) so may not be entirely perfect for your needs.
The blooming of the French lilac -- Witters 108 (8): 1105 -- Journal of Clinical Investigation. Lee A. Witters. Endocrine-Metabolism Division, Departments of Medicine and Biochemistry, Dartmouth Medical School. Lee.A.Witters@Dartmouth.EDU