Unfortunately you can't have it both ways if you want an OS level language setting. The software (word processor or internet explorer) has to support the dual mode keyboard.
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OS Level Setting (You will need your OS Disc to install Asian Languages.)
Control Panel --> Regional and Language Options
Regional and Language Options overviewWith Regional and Language Options in Control Panel, you can change the format Windows uses to display dates, times, currency amounts, large numbers, and numbers with decimal fractions.
You can also choose from a large number of input languages and text services, such as different keyboard layouts, Input Method Editors, and speech and handwriting recognition programs. When you switch to another input language, some programs offer special features, such as font characters or spelling checkers designed for different languages.
By default, products in the Windows .NET Server family install the files for most input languages supported by Windows. However, if you want to enter or display text in the East Asian languages (Chinese, Japanese, or Korean) or the complex script and right-to-left languages (Arabic, Armenian, Georgian, Hebrew, the Indic languages, Thai, or Vietnamese), you can install the language files from the Windows CD-ROM or, if applicable, a network.
Each language has a default keyboard layout, but many languages have alternate versions. Even if you do most of your work in one language, you might want to try other layouts. In English, for example, typing letters with accents might be simpler with the U.S.-International layout.