If you have patched your uxtheme.dll already, and want to see one of Windows XP's early themes...i have attached it.
You must remember, this was quite a development from the usual grey color and got us where we are now with Luna, and it also played a part in what Vista will look like.
Though XP was important, without it there would be a gap and Vista wouldn't be such a development or step forward.
Anyway, just run the setup and it will do the rest, it won't work unless you patch your uxtheme.dll or already have done so.