The TSF tour ends here, with a brief discussion of UI Elements in Vista

If your text service wishes to be available in full-screen applications like games, it must implement ITfUIElement, and call the ITfUIElementMgr whenever the text service wants to display some UI. (See the discussion of UILess mode in MSDN.)

Interface

How Obtained

ITfUIElement

Passed to ITfUIElementMgr::BeginUIElement

ITfToolTipUIElement

QI from ITfUIElement

ITfCandidateListUIElementBehavior

QI from ITfUIElement

ITfCandidateListUIElement

QI from ITfUIElement

ITfReadingInformationUIElement

QI from ITfUIElement

Text services that implement  ITfUIElement should also register in the GUID_TFCAT_TIPCAP_UIELEMENTENABLED category, as well. 

Unfortunately, as of this date, I do not know of any sample text service that implements ITfUIElement.