You mean running both screens of the same card ? expect issues
, or a lot of tweaking of the xorg.conf , I always use 2 cards 1x AGP + a PCI , I did get twinhead happening with an ATI Radeon 9200 on Xandros but on Fedora I have to use another PCI card before dual monitors work properly for me.
I think the distro you use is as important as anything , Fedora always gives me issues with anything other than basic config (it can detect all the adapters but enabling them does not always work)
Xandros (debian based) is almost as easy as win32 though you cant move your monitor arrangement without playing with the xorg.conf (easier to physically move the monitors
) , Ubuntu (also Debian based) is just as good , that tells me something , though I have never had much luck with an out of the box deb ian solution?