Tested on Vista x64 build 5384, Japanese.
Launch SwingSet2 demo then in InternalFrame demo, try using native IM and you'll find that you cannot. Same happens in Table demo but not in those invokes separate dialogs such as FileChooser or OptionPane demos. This problem wasn't there in Vista build 5308, English. Please let me know what information is needed to evaluate this bug.
Here are our observations.

- The symptom is not reproducible on the English version of Vista.

- In English-US locale setting on the Japanese version of Vista, the symptom is reproducible.

- The symptom is not reproducible with Notepad and Stylepad.

- The symptom is not reproducible with a Dialog window popped up from SwingSet2.

- Switch to English input mode and back to Japanese input mode. Then, the symptom is gone.