The usual is the Themes service. There may be others.
Here's a screenshot. You can see how some aspects of the OS are changed (because of the theme), but the taskbar looks like it's in classic mode
I've tried applying the theme with StyleXP, but it wasn't compatible with my build of XP. I've also tried using TuneUp Utilities Styler, but that didn't help either. I've checked Taskbar->Properties->Start Menu, and it was set to "Windows XP", not classic.
I've even tried changing my theme to "Windows XP" (it IS an option), but that still doesn't change the taskbar. It changes everything else EXCEPT the taskbar. Does anyone have any idea as to what I can do to solve this?
I've tried several themes, all with the same results.
PS: I have patched the UXTheme.dll.