knoppix 3.4. It is the standard by which I will test laptops before I install on them. That is an older computer, found a review with Redhat 6.2 on it at linuxlaptops, which is good in the sense that older hardware may well have reverse engineered driver support. Try knoppix, you will know what hardware will work.
You can also look at similar machines to see if the same modem has worked on newer models.
Given the specs...475 MHz with 64 Meg of Ram, Fedora may be a little heavy, at least with either Gnome or KDE. You will likely want to install the lighter window managers during the install.