From what I understand (please correct this if any information is incorrect), drivers and codecs must be 64-bit to function on Windows XP Professional x64 Edition.

32-bit software that are not drivers or codecs and compatible with Windows XP Professional may run on Windows XP Professional x64 Edition through emulation.

Are theme styles for32-bit Windows XP and Windows Server 2003 (Luna, Windows Embedded Standard, Zune, Royale, Royale Noir, etc.) operating systems compatible with Windows XP Professional x64 Edition?

Is there a software scanner or index that may be used to determine whether a software codec is 64-bit compatible?

You can install 32 bits codecs if you use a 32 bits player that use these codecs.

For themes, i don't know.