Here are some regedit hacks that let you customize the Bubble screensaver in Vista. To use them start the registry editor (type regedit in the Start search box) and on the left side of the editor navigate to the HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Screensavers\Bubbles section.

Once there, you'll then need to create new values for several settings that can be adjusted. Each new value is created by right-clicking in the right side of the pane and selecting New -> DWORD (32-bit) Value and then entering a name and a value for the value (you'll probably have to double click on the entry to enter the value). The entries that can be created for the Bubbles screensaver are:

MaterialGlass => Enter a value of 1 for bubble that look glassy, or bubble-like, 0 for metallic looking bubble.

ShowShadows => Enter a value of 1 to show the shadows of the bubbles, 0 for no shadows.

ShowBubbles => Enter a value of 1 to show the bubbles on the desktop, 0 to show them against a black background.

Once you make you changes, you need to reboot for the changes to take effect.