Problem: No sound in Windows Vista even after installing the Boot Camp drivers found on the Mac OS X Leopard install disc. Additionally, updating Vista via the Windows Update application (even updating to SP1) fails to fix the problem. Resolution: Download and install the Boot Camp 2.1 drivers for Vista (64-bit here, 32-bit here). Thought this might help others in the same situation as me. My 24" iMac was fixed after doing this.