I have a 8510w as well and this problem with closing the lid is killing me. Whats worst is that sleep and hiberate don't work i.e. goes to sleep but lights and CPU/Fan/USB still on.
I am also running Kalyway 10.5.2 and also tried patching to 10.5.5, iDeneb 10.5.4, Retail 10.5.6 (with EFI), patched my DSDT and every other imaginable fix, kernel (voodoo, sleep, speedstep etc) and kext (Insomnia, Clamshell, Shutdown/Halt etc etc) and no joy.
Did you do anything special when you installed Kalyway 10.5.2?
Whats interesting for me is that when installing OS X with media for Kalyway, iDeneb and Retail DVD you can close the lid while it's booted up. I tried using the kernel and Extensions.mkext off the DVD but didn't solve the problem which points to some software or configuration item.