I assume you are talking about either and older Red Hat, Mandrake, or SUSE distro. I no longer have Linux installed on my Gen 1, but I used to have Mandrake and Yoper installed on a partition. I set up a LILO boot-loader to load either WinXP or Linux on bootup.
If you want to dual-boot, you will first have to re-partition your 100GB drive and reserve maybe half of it for the 4 Linux partitions you will need. The video drivers for the ATi card were kind-of weak back then, but I bet they are much better now since ATi supports Linux now.
Once you free up some space for Linux, the install should be pretty straight foward unless you try an obscure distro. You may want to stick with the 2.4.x kernel since the Gen 1 is older hardware.