styleXP is an option, or the slightly harder method which is entirely free & takes 0 bytes of space on your disks is the following:
unzip this for XP without SP1 or this for XP with SP1 to a temporary folder.
rename uxtheme.dll to uxtheme.new
move it to c:\windows\system32
reboot into the recovery console (boot the windows install cd, eventually you can press r to go itno the console)
type
Code:
cd system32
copy uxtheme.dll uxtheme.old
copy uxtheme.new uxtheme.dll
copy uxtheme.dll dllcache
exit
you can now extract skins to c:\windows\resources\themes and actuvate them using the inbuilt windows xp skin changer (where you change Classic or Luna theme) in the display control panel
.THEME files belong in \resources\themes and dictate a number of settings such as what skin to load, what icons & sounds & wallpaper to use, etc
skinname.MSSTYLES lives in \resources\themes\skinname - and skins can't be reached unless they meet this directory structure.
there you go, Xp skin 101. have fun, and try not to break anything