Is it possible to type traditional characters with a pinyin IME in Windows 7?
Here's one way to do it which I figured out starting from some tips thanks to user2619 in the comments:


Right click on the keyboard/IME icon in the system tray.
Select "Settings" from the popup menu.
The "Text Services and Input Languages" dialog will appear. Use the "General" tab.
Under "Installed services" click on "Add...".
Find the section "Chinese (Traditional, Taiwan).
Select "Chinese (Traditional) - New Phonetic". Click "OK".
Left click on the keyboard/IME icon in the system tray. Select "Chinese (Traditional, Taiwan)".
Click on the "Tool Menu" icon in the IME's system tray icon. It's the 4th icon to the right of the CH icon.
Select the "Properties" menu item. Then the "Keyboard" tab.
In the section labelled "Choose your preferred keyboard layout", choose "HanYu Pinyin" from the dropdown list.


Now if you are used to the Pinyin IME for simplified Chinese in the PRC the way to select characters is totally different. I haven't figured out that part yet ...