I'd suggest some proper software rather than random software (there are tons of theme programms around).
(And most of them are shit tbh).
I recommend using TuneUp.
Its not only a system maintance tool but also allows customization without patching and crap.
(Icon size, Space between Icons, Shortcut Icon removal, Custom Bootscreen/Logonscreen, Icon set, Styles etc.)
TuneUp Homepage /
Customize Information
Reads most of the xp containers/packs so its not restricted to some fancy type.
And you dont have to reboot for a change of your theme.
Using it myself altough a older version xD (tuneup 2007).