This document, although gentoo related, might help you: (it helped me)
You need to load, in this order: agpgart, [nameofchipset]_agp, fglrx. once this is done, you need to fill the kernel dependencies (such as installing the right kernel/modules), and you are usually done.
Oh, it's has to be the right chipset agp driver, otherwise, it won't work. You need to load the ati agp module is it's a IGP card. check lspci if you aren't sure