Loaded into the Windows 7 Beta system are a few Themes that are not loaded by default.

I've tried this and it does load them up into the Theme selection process.

Copy this and place into a .reg file -

Code:
Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Themes\InstalledThemes\MCT]
"%windir%\\Globalization\\MCT\\MCT-AU\\Theme\\AU.theme"=""
"%windir%\\Globalization\\MCT\\MCT-CA\\Theme\\CA.theme"=""
"%windir%\\Globalization\\MCT\\MCT-DE\\Theme\\DE.theme"=""
"%windir%\\Globalization\\MCT\\MCT-GB\\Theme\\GB.theme"=""
"%windir%\\Globalization\\MCT\\MCT-JP\\Theme\\JP.theme"=""
"%windir%\\Globalization\\MCT\\MCT-US\\Theme\\US.theme"=""
"%windir%\\Globalization\\MCT\\MCT-ZA\\Theme\\ZA.theme"=""

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Wallpapers\0\KnownFolders\Windows Wallpapers\MergeFolders]
"%windir%\\Globalization\\MCT\\MCT-AU\\Wallpaper"=""
"%windir%\\Globalization\\MCT\\MCT-CA\\Wallpaper"=""
"%windir%\\Globalization\\MCT\\MCT-DE\\Wallpaper"=""
"%windir%\\Globalization\\MCT\\MCT-GB\\Wallpaper"=""
"%windir%\\Globalization\\MCT\\MCT-JP\\Wallpaper"=""
"%windir%\\Globalization\\MCT\\MCT-US\\Wallpaper"=""
"%windir%\\Globalization\\MCT\\MCT-ZA\\Wallpaper"=""
Then just double-click the file and you'll have a few more themes to play with.


Just to add. Microshot has also finally opened the Windows 7 beta website properly.
Some interesting updates starting to show up -
http://windows.microsoft.com/en-GB/Windows7/Personalize