no sound in dual booted Windows 7

Check in Device Manager to see if there are any next to your devices. It probably doesn't have the driver installed.

Depending on the age of the XP hardware, there are some older sound modules that are not Windows 7 compatible. If the sound hardware was compatible, Windows, in most cases, will at least install the generic, basic function, "High Definition Audio Driver". If that was not installed, there is a good chance the XP hardware is not compatible. (And in almost all cases the XP sound driver is not Windows 7 compatible. You need at a minimum Vista specific sound drivers).

If the sound device is not compatible, your ONLY option is to install a Windows 7 sound card (if this is a desktop) or a USB connected sound card. Compatibility was a major issue back when Vista came out as there were many users that upgraded to Vista only to find out the sound hardware was not compatible.