i have experience with hybrid
System
GIGABYTE GA-MA78GM-S2H
AMD Phenom 9600BE
CORSAIR DOMINATOR 4GB DDR2 1066(2 x 2GB)
SAPPHIRE Radeon HD 3450 512MB
SILVERSTONE SST-ST56ZF 560W
Windows Vista Ultimate 64-bit
now, setup uses the IGP as the initial display in bios (using hdmi to a Samsung 61" DLP no less)
using cat8.3, in 'advanced mode' (in other words, access to all options, to be honest, i've never seen what the basic mode looks like, lol), there should be an option for crossfire, once you click that, you'll be given some dialog and a check-box, simply check the box, screen should flicker, and that's it
tested with 3dmark06
all settings stock (ram running at ddr2 800)
IGP alone was about 1500 marks
Discreet alone was about 1800 marks
IGP+Discreet was just over 2700 marks
when in 'hybrid xfire', i was able to oc the IGP from a 500mhz core speed, to 625, and scored just over 3000 marks
unfortunately, i haven't been able to stable anything over 625mhz on the IGP, and have gotten 0 response from anyone on support for overclocking the 3450, much less both in crossfire
too bad too, because the scaling seems to be awesome
btw, this setup all at stock (using hybrid xfire) does play quake4 at ultimate graphics at some 1920x1080 res, playable, and on a 61" samsung DLP, it is a beautiful thing
again though, wish there was more support for overclocking, though i guess that will come with some time
also, not my setup, this is a setup i put together for a friend, so any questions might take a day or 2 for me to answer
also, I've read that hybrid will only work with Vista, and AMD Overdrive latest version is supposed to support Hybrid Crossfire as well, but does not seem to support Vista 64, in fact, when I try to run it, it says 'Cannot detect AMD CPU', hahahaha, so, again, more waiting for support