1) Using Windows Explorer, go to the installation folder you have chosen on your PC. You should see files with the '.tsk' extension - these are your theme files.
2) Open Microsoft ActiveSync and click on the Explore button (once your Pocket PC is connected to the PC).
3) Copy your theme file from your computer to your Pocket PC My Documents folder.
4) On your Pocket PC Tap Start > Settings> Today, and click on the Appearance tab.
5) On your Pocket PC, tap Start, Settings and Today and select the theme you want to use.
6) Enjoy your new theme.