I've always had the 100% CPU problem, even when using kernels besides phatk. From what I understand it's a bug in Catalyst, not so much a kernel thing. I've tried Catalyst 11.5, 11.6, and 11.7 and and they all do that on my Win7x64 box.
I realized, that with the new 11.7 drivers, I now have the cpu bug, too. even with poclbm

so I switched back to 11.6, and now everything works perfect without using the cpu.
I wonder, that you always experience that problem, cause I run win7 64x ultimate, too and with the 11.6, sdk 1.4 and poclbm I don't have that problem. the older versions (11.4 and 11.5) worked also without the bug...
cheers iro