hey there.
let's make it clear: the 10.6.2 drivers ARE 64 bit. better said 32/64 bit, depending your booted kernel.
i don't know, how did you copy the 10.6.2 kexts and exactly what files did you copy over to /S/L/E
before trying to use some heavy gfx intensive stuff (mission control, safari with embedded videos, etc),
just open up a terminal window, and type the following magic commands and post us the results so we
can make sure you are really running the wanted version kexts:
iMac:~ user$ kextstat | grep ATI
you shall see something similar:
81 2 0xffffff7f80ebf000 0x45000 0x45000 com.apple.kext.ATISupport (6.0.6) <74 9 8 7 5 4 3 1>
82 0 0xffffff7f80f04000 0xca000 0xca000 com.apple.kext.ATI2400Controller (6.0.6) <81 74 9 8 5 4 3 1>
92 0 0xffffff7f81189000 0x261000 0x261000 com.apple.ATIRadeonX2000 (7.1.2) <75 74 9 7 6 5 4 3 1>
97 0 0xffffff7f814b2000 0x12000 0x12000 com.apple.kext.ATIFramebuffer (6.0.6) <81 74 9 8 7 5 4 3 1>
with exception of ATIRadeonX2000 (ver. 7.1.2) all the others came from 10.6.2.
just to be sure: if you copy over the files to /S/L/E, no matter how you do it, osx rebuilds the kernel caches. one has to wait couple of seconds (maybe minutes) to make sure, those caches are really rebuilt.
osx refuses to load kexts, which are not owned by user root & group wheel, and shall not have extended attributes (can be checked with ls -l@).
basically this two failure scenarios can be avoided by fixing permissions (which takes time up to 2-3 minutes) or by issuing this commands in terminal:
sudo chown -R root:wheel /System/Library/Extensions/ATI*
sudo xattr -src /System/Library/Extensions/ATI*
but first, just send in the kextstat output. in case you need i can provide you the kexts.