Найдите, которому диск соответствует который устройство массового хранения USB в WinXP

It's a non-trivial question. There is no official API for it, as far as I can tell. So, you need an undocumented API: the registry. HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices contains entries for both drive letters and volume IDs. If you look at the actual data, you'll find that it identifies the drive. Look at the binary data as a Unicode string. It will point you to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\ENUM\. However, XP and Vista differ in exactly what subkeys are referenced there, and how. (Vista is easier, so try that first).