To get your truecolor modes on the Radeon you just need to open P96Mode and toggle the color depth gadget on your truecolor modes to Truecolor+Alpha.
Regarding Radeon 9200 being slow, there seems to be a bug in P96mode when you change graphics cards it sometimes converts to nonsensical refresh rates and/or pixel depth modes, sometimes this makes modes run really slow or causes crashes even though initially it seems like it is working. Best option is to just recreate the modes, which is really easy with the Radeon on DVI since you pretty much just put in 60Hz vertical and most of the time it will work with minor tweaking.
