How can I change the default Windows 7 sounds to Windows XP sounds?
Windows sounds are located at C:\Windows\Media. Locate the files in XP and copy them to your win7.
Make up the theme how you want it;
http://windows.microsoft.com/en-AU/windows7/create-a-theme
And then save the theme. Make sure to save the theme for sharing so that you can save a copy somewhere so you never have to manually create it again.