Just a brief recap of this cards functionality under OSX.  Under Tiger this card is capable of full resolution switching  using Callisto drivers, I used callisto 006 for this.  Also QE and CE are availble by adding the device ID (availble by looking in system profiler) to the ATIRadeon9700.kext.  The string to be added will be your device ID plus the vendor ID and should be in this format (XXXX=your device ID) 0xXXXX1002 .  Under some versions of Tiger you will experience mouse tearing. 

    Under Leopard there is no QE or CE for this card as it requires newer Functions to operate the enhanced QE and CE in Leopard.  However the same procedure should be followed to initiate as many of the features as possible under Leopard.  Callisto drivers should still be used for resolution switching, and adding your device ID to the ATIRadeon9700.kext does not hurt anything. 

    Just make a post if you need further instructions.

Meaning functions the 9550 doesn't have and never will.  Newer graphics card with fancier tricks is required to use QE/CE in Leopard.  As a guess you will probably need ati x1000 or new card.  7000 or better Nvidia probably.   Don't quote me on the exact requirements they are somewhere around there for OSX 10.5 Leopard.