On older Celery 400Mhz machines, ATI Rage video cards, everything-on-board Gateway PCs I found small quirks with both Mandrake and Suse installs. I would say try Redhat 9.0 or if you just want to have a look try Knoppix (it runs straight from CD with about 2Gb of apps to play with).
I've used RedHat9 on both a modernish Duron/Athlon machine and an old grunter of a P233 mostly fine (see later). However there *was* a problem with the 2.4.20 linux kernel and *some* Athlon/XPs (especially XPs - including mine) which seeing as it was the "current" kernel affected Redhat9, Madrake 9.?, Knoppix 3.2 and so on, maybe this is your problem?
I'd say get and try Knoppix 3.3 (newer kernel) and if that works this may be the answer. Until the Athlon XP problem was fixed Redhat9 had freezing on boot, and some executables on Gentoo just crashed. Since Gentoo has been updated to a newer kernel it is fine. As for internal modems, "Winmodems" are not usually linux-friendly, graphics cards - sorry don't know much about the specifics here.