Mesa (the open source 3d stack) doesn't support 3d acceleration for your card at present, but support should (hopefully) be coming soon.
The radeonhd and radeon drivers are actually fairly similar, but differ in how they do modesetting. Radeonhd does modesetting using the card's native registers (when possible, it also has support for atombios), which has the advantage of being fast and "open," but the disadvantage of being harder to program. Radeon uses atombios exclusively, which makes the driver easier to write, but depends on the (sometimes buggy) atombios interpreter of the card to function, which is also a bit slower (for modesetting.)
Last edited by TechMage89; 09-08-2008 at 10:21 PM.
No, Xv is tearing no matter which driver you use. The only way to have tearless video is to use Gl instead of Xv and enable vsync, and this requires fglrx since neither radeon nor radeonhd support direct rendering on the 4xxx cards.
On the 4xxx cards, radeonhd defaults to AtomBIOS (as seem in X's startup log).
Note that this patch works by stalling rendering until the scanning line is passed, meaning it's sort of a hack and might cause jittery video performance for lower-end cards. The ideal way to vsync is to double-buffer, but that's a lot harder to implement.