Can't tell you about the radeon, but the Fedora Core 1 does support serial ATA (at least mine works fine).
If I was you I'd be tempted to follow the route I've used. I made my PC dual boot leaving my XP Pro on. My idea being that while I'm learning linux if I screw anything up I've still got an OS to fall back on.
This had proved to be worth while as at the moment my linux n/work card is screwed up and isn't working, so I can use my XP to browse the forums and internet to try and find out why otherwise i'd be lost.
Ultimately I'd like to ditch the microsoft, but just now I don't have the confidence in myself. Be nice to have to machines both running linux.
Gotta take the plunge sometime