Ok so first I would like to say that I had this problem for about a day and looked all over the internet for answer. I found one solution to another and some were down right silly. Just to let everyone know I have an iMac 27 2.8 quad core. I finally worked through the trials and tribulations of actually getting Win7 installed and when it booted up I had no sound. From what I have read online many people are having this problem. A quick way to tell if you are having the same problem I was is if you look at the back of you iMac 27 and notice a red light coming out of your mini jack port. If so this is what you need to do. I went into device management (in windows 7) and uninstalled the two drivers that were under my sound device. After that I inserted the Snow Leopard Disc and I right clicked and Opened it (not run it). Went under the drivers area and loaded the vista64 realtec drivers. After the installation I rebooted and noticed that the red light was no longer on in the back and the sound worked. Hope this works.