If you have installed the boot camp drivers correctly, the speakers and audio jack should work fine, to the equivalent of OS-X. Are you able to perform other boot camp tasks, such as adjusting screen brightness via the keyboard, etc? If not, reinstall the boot camp drivers.
To install the boot camp drivers, load Boot Camp Assistant on OS-X, and "Download Support Drivers to Memory Stick or DVD". Reboot into your Windows partitions, and open the executable file from the memory stick/DVD.