Caching one section of a CodeIgniter page
Take a look at the query caching page, or alternatively you can use a caching library to cache sections of a page (preferred method IMHO) take a look at KhCache.
Another good caching library I have found is from Phil Sturgeon. http://github.com/philsturgeon/codeigniter-cache
It allows caching models, libraries, or just partial caching like you describe.