(There's no video for Theme Changer (OSX theming) yet. Please contribute to MR and add a video now!)
ThemeChanger switches your theme in Mac OS X 10.2, 10.3 or 10.4 and it supports the .theme and .dlta formats.
For other themes such as in the guikit format, see: ShapeShifter
themechanger-0-6-1.dmg (289.15 KiB / 296.09 KB)
Theme Changer v0.6.1 for OSX 10.2 to 10.4 / DMG image
Mac OS X 10.2 - Mac OS X 10.4
Emulating this? It should run fine under: SheepShaver