@shldr2thewheel: Nice catch. As soon as I read that, I remembered being rather irate one night that I had to re-install XP and couldn't use my pretty new Win 7!
@The hatter: Lots of great info there as always. I avoided Vista like the plague but heard LOTS of complaining and general gnashing of teeth about stuff. Good to see it getting resolved.
@Sean_Bishop:
Honestly, if you've already repartitioned the drive and gotten Windows to install, then you've gotten through 90% of what trips everyone up. This last part is actually pretty straight-forward — kinda long, sure, but straight-forward.
1. Boot the machine into Windows and insert the OS X Install disc. (From the sound of it, you're using Snow Leopard? BTW, is that the version that came with your iMac or did you upgrade after you got the machine?)
2. Open Windows Explorer (file browser) and explore the contents of the install disc.
3. Locate the file called "BOOTCAMP.msi" and copy it to a folder on the hard-drive.
4. Go to the copy on the hard-drive, right-click (control-click) the file and select Properties.
4. In the Properties window, select the "Compatability" Tab. You should see something like:

(I believe this is actually a Win 7 window but it should be very close to the same thing.)
5a. Make sure that either (a) Compatibility mode is disabled or (b) your version of Windows (e.g. Windows Vista + any service packs) is selected in the drop-down. (This forces the OS to run the installer with the proper version so it loads the correct drivers, btw.)
5b. Enable the "Run this program as an administrator"
5c. Click OK to close the Properties window. (If it complains that the file is read-only or says you can't change the Properties, be sure you're playing with the copy and not the original on the DVD.)
6. Double-click the BOOTCAMP64.msi file to install (or re-install, doesn't matter) the drivers
7. When it's done you'll need to reboot the machine into Windows again and check for the BootCamp icon in the system notification area (the bottom-right corner where the clock is). The icon is a dark-grey square up on one corner; if you click it is comes up with a few options, one of which is "Reboot into OS X" -- (that's a pretty good indication it's the right icon!)
8. If the Window's side of BootCamp is installed, try the sound out. Play a known good video or sound file, or go to the Sounds control panel.
9. If the sound is working you have the option of stopping (obviously since that was your original goal!) or you can try the next step to ensure you've got the "best" driver.
10. If the sound isn't working or you want to search, you can go to the Device Manager (accessible through the Control Panels menu or by right-clicking / control-clicking My Computer in the Explorer and selecting "Manage this computer"). The Device Manager will show you a list of all the hardware in the machine with alerts to which ones aren't installed or can't work.
11. Find the sound chipset (sounds like yours is from Cirrus) and get the model/version of the chip. Then head to Google and search for that model and be sure to add something like "Windows Vista 64-bit drivers". You can then manually download and install that driver per usual. (I say usual because hunting for the best drivers is a skill that every savvy Windows machine owner learns to do at some point. lol)
Note: standard disclaimer about downloading stuff from the Internet applies. Pick a good, reputable site that you trust, etc.
It sounds like a lot but it's really not that bad.
Good luck and be sure to let us know how it goes.
Hoji.